How to Increase Email Deliverability in 2025 Using AI – Without Sacrificing Scale

Major Takeaways: Increase Email Deliverability

Build Sender Reputation with Proper Email Warm-Up

• Gradually increasing send volume and generating positive engagement can improve inbox placement by 20–25%, based on real case studies.

Use Inbox Rotation to Scale Without Triggering Spam Filters

• Sending from multiple warmed accounts lowers per-inbox volume and reduces the risk of blacklisting or domain throttling.

Embrace AI Tools for Email Deliverability Optimization

• AI platforms can automatically manage send schedules, verify addresses, and adjust to ISP rules—boosting open and reply rates by up to 30%.

Avoid Deliverability Pitfalls with List Hygiene and Authentication

• Email lists decay at an average rate of 23% per year. Regular validation and SPF, DKIM, DMARC setup are essential to maintain high inbox rates.

Monitor Key Metrics to Protect Sender Health

• Bounce rates over 2% or spam complaints above 0.3% can severely damage deliverability. Active monitoring ensures quick course correction.

Optimize Email Content to Avoid Spam Triggers

• Personalized, concise emails with non-promotional language improve deliverability. Subject line testing and compliance checks are vital in 2025.

Use Omnichannel Outreach to Reduce Email Overload

• Combining email with LinkedIn and phone reduces reliance on any single channel, leading to a 31% higher lead conversion rate on average.

Partner with Experts to Maximize Deliverability ROI

• Outsourcing to deliverability-focused sales agencies like Martal can yield 2x higher ROI and 6.6x more qualified replies by applying best-in-class infrastructure and strategy.

How many of your outbound emails are actually reaching prospects’ inboxes? In B2B sales, a message that never lands is a missed opportunity. Email remains a powerhouse channel for SDRs and sales teams, but success hinges on one critical factor: deliverability. In fact, roughly 1 in 6 marketing emails failed to reach recipients’ inboxes in 2024 (2). Spam filters have only grown more sophisticated, and major providers like Gmail even tightened bulk sender guidelines in 2024 – requiring authentication, easy opt-outs, and ultra-low spam complaint rates (4). If you’re wondering how to increase email deliverability in 2025 without throttling your outreach, you’re not alone. 

This guide will show you how to scale outbound campaigns while keeping emails out of spam, using the latest best practices and AI-driven tools. We’ll explore:  

• Scaling outreach without sacrificing deliverability, 
• AI-powered techniques to boost inbox rates, and 
• the 2025 playbook for email warm-up & inbox rotation to build sender reputation.

Along the way, we’ll highlight how Martal Group – a leader in B2B sales lead generation – applies these strategies (via an AI-powered platform for email warming, inbox rotation, and omnichannel outreach). By the end, you’ll have a roadmap to increase your email deliverability rate and connect with more prospects. Let’s dive in!

Why Deliverability Matters More Than Ever in 2025

Deliverability isn’t just an “email geek” metric – it’s the bedrock of successful outbound sales. If emails don’t land in the inbox, they can’t be opened or replied to, stalling your pipeline. And the stakes are rising: 78.5% of email marketing specialists now rate deliverability as “8 out of 10” or higher in importance (3). High deliverability means your carefully crafted B2B cold email actually gets seen by decision-makers, giving you a chance to start conversations. Low deliverability, on the other hand, can quietly sabotage your entire outbound  lead generation effort. Consider that global spam rates nearly doubled from Q1 to Q4 2024 (2) – a sign that inbox providers are cracking down harder on unwanted emails. If your emails resemble spam (or if you accidentally trigger filters), they’ll join the millions of messages that never make it to the inbox each day.

Providers are enforcing new rules: Google, Yahoo, and Microsoft have all introduced strict sender requirements. Starting in 2024, Gmail began requiring any sender blasting out 5,000+ emails per day to Gmail addresses to authenticate their domain (SPF, DKIM, DMARC), include a one-click unsubscribe link, and maintain a spam complaint rate below 0.3% (4). Yahoo implemented similar standards, and by March 2025 Microsoft Outlook joined in with its own bulk sender rules (4). The penalty for non-compliance is severe: your emails will be blocked or sent to spam, and your sender reputation will plummet (4). These industry shifts send a clear signal: quality over quantity. As one analysis put it, “Personalized, authenticated, well-targeted outreach strategies is the new standard” (4).

Even without these rules, the physics of email deliverability favor careful senders. High-volume blasts from a single domain can crush your inbox placement. For example, companies sending over 1 million emails per month saw their average inbox placement rate plunge from ~50% in early 2024 to just 28% by early 2025 (1). Why? ISPs and spam filters get very suspicious of domains that suddenly spray out huge volumes or get low engagement. It’s not just big senders at risk; even smaller sales teams must monitor deliverability metrics. A sudden drop in open rates toward zero is often a red flag that your emails are being junked (2). And spam complaint rates above ~0.3% (that’s just 3 complaints per 1,000 sends) are enough to harm your reputation over time (2). In short, inbox placement is mission-critical: one study found 33% of recipients feel disappointed when a company’s message lands in spam, and 10% lose trust in the brand when they repeatedly see emails caught by filters (2).

Key takeaway: The landscape of email deliverability in 2025 demands attention. Deliverability directly impacts pipeline and revenue, yet many teams still underestimate it. (Around 9% of professionals don’t even understand sender reputation or its impact (2).) Don’t let your outreach efforts go to waste. In the next sections, we’ll cover how you can scale up your outbound emailing while staying on the right side of spam filters – leveraging smarter tactics and tools to ensure your emails reach prospects’ inboxes.

Scaling Outbound Outreach Without Sacrificing Deliverability

Every sales leader wants to reach more prospects, but scaling outbound email can feel like walking a tightrope. Send too little and you limit your pipeline; send too much (or send carelessly) and you could burn your sender reputation, landing in the dreaded spam folder. So, how do you increase email deliverability rate while also increasing volume? The answer: strategically and gradually. It is possible to scale your outreach without sacrificing deliverability – but it requires the right approach.

First, recognize the trade-off between quantity and quality. Blasting out generic emails to massive lists is a recipe for low deliverability. It’s telling that nearly 45% of outbound campaigns fail to generate a single lead (8), often because overly aggressive, untargeted emailing backfires. Scale alone won’t drive results if emails never make it to inboxes or fail to resonate. Instead, focus on sending better emails, not just more emails. By improving targeting and content, you can maintain engagement even as volume grows. High engagement (opens, replies) signals to mailbox providers that your emails are wanted, which boosts deliverability.

Best Practices to Scale Safely: Before you ramp up your send count, put these foundational practices in place:

• Use Multiple Sender Accounts (Inbox Rotation): Don’t have all your emails coming from one email address or domain. By rotating senders across multiple domains or inboxes, you spread out volume and reduce the load on each sender. This lowers the chance of any single address getting flagged for unusual activity. For example, an SDR team might use 5–10 different email accounts (across one or more domains) instead of just one, distributing the campaign sends among them. Martal Group’s platform takes this approach – it can send sequences across custom domains to keep your primary domain safe (9). If one domain or IP hits a daily limit or gets a temporary block, the others continue operating, ensuring continuity. The result: you can send a higher total volume collectively without any single domain tripping alarms.
  
• Warm Up Every Domain and IP: (We’ll dive deeper into warm-up shortly, but it’s worth staρting up front.) Never start blasting cold emails from a brand-new email domain or IP address. Build up sending reputation gradually. Start with a low send volume (e.g. 20 emails/day per new account) and increase over a few weeks (6). During this warm-up phase, sending emails to highly engaged contacts (or using an automated warm-up service) is essential to generate positive interactions. This process “seasons” your sender reputation so that when you do scale to hundreds of emails a day, you’re not immediately tagged as spam by ISPs that see a sudden spike from an unknown sender.
  
• Monitor Key Metrics and Adjust: You can’t manage what you don’t measure. Keep a close eye on deliverability metrics like bounce rate, spam complaint rate, open rate, and reply rate. A bounce rate higher than ~2% is a warning sign (5) – it means you’re hitting too many invalid addresses (hurting your reputation), so you may need better list hygiene or email verification. A spike in spam complaints (even a few out of a thousand emails) should prompt an immediate pause and investigation – which email or segment triggered people to hit “Report Spam”? Many savvy outbound teams set internal thresholds (e.g. pause a campaign if spam complaints exceed 0.1%). Even open rates serve as a proxy for deliverability: if a normally engaged segment suddenly drops to near 0% opens, your emails might be getting junked. 63% of businesses now adjust their email sending frequency based on engagement levels (5) – for instance, slowing down or pausing sends to cold segments while focusing on engaged contacts. This kind of agile adjustment helps protect your sender reputation when something looks off.
  
• Practice Good List Hygiene: Scaling outreach doesn’t mean blasting anyone with an email address. In fact, pruning your lists can increase deliverability. Remove or suppress contacts who never engage after several touchpoints – continuing to email uninterested or invalid addresses will drive up bounces and complaints. Ensure every address you contact was acquired legitimately (e.g. via a prospecting tool or inbound lead) and is periodically verified. According to industry data, approximately 23% of an email list goes “bad” each year (due to people changing jobs, abandoning addresses, etc.)(5) . If you don’t weed out those hard bounces and non-responders, your sender reputation will suffer over time. Use email verification services and consider a double opt-in for any web form leads to ensure quality.
  
• Limit Send Frequency and Volume Per Account: As you scale, be mindful of how many emails each account sends per day and per hour. Sending in large, irregular bursts can trigger filters (10). Instead, send in consistent batches and stagger send times. For example, rather than one account sending 500 emails at 8:00 AM sharp, it’s better to send ~50 emails/hour over 10 hours, or distribute those 500 emails across 5 accounts sending 100 each. 

Many email providers have implicit hourly and daily sending limits – exceeding those or suddenly approaching them can cause deferrals or blocks. A common rule of thumb is to keep well below Gmail’s known free account limits (~500/day) or business account limits (~2,000/day), unless you have a warmed dedicated IP setup. It’s also wise to give each inbox “rest” days or lower-volume days if you’re pushing the upper limits, allowing reputation to recover.

• Personalize and Add Value: This might sound like marketing fluff, but it’s critical for deliverability. Boilerplate spammy emails will get ignored or flagged. High-quality, personalized emails tend to earn more opens and fewer spam reports, which in turn boosts your sender reputation. Even simple personalization – using the prospect’s name, referencing their company or pain points – can lift open rates (personalized subject lines alone can increase opens significantly, by ~10–14% in some studies (10)). Avoid spam trigger words and gimmicky formatting that might trip content filters (phrases like “100% FREE!!!” or excessive exclamation points and all-caps (11)). While modern spam filters weigh sender reputation far more than the actual words, extremely promotional language can still hurt. Focus your message on the prospect’s needs and how you can help, rather than hard selling – this not only improves response rates, it also reduces the likelihood of recipients marking you as spam.
  
• Leverage Omnichannel Touches: One clever way to reduce heavy reliance on email (and thereby protect your deliverability) is to use omnichannel outreach. If you’re also reaching out via LinkedIn, phone calls, and other channels, you don’t need to bombard someone with 10 emails in two weeks. A few well-timed emails combined with LinkedIn messages and maybe a call can suffice. In fact, multi-channel sequences are proven to convert higher – 31% higher lead conversion rate than single-channel, on average (9). Martal Group’s outbound programs employ this balanced approach: for instance, an SDR might send an intro email, then connect on LinkedIn and engage there, then perhaps a call, before sending a second email follow-up (9). By spreading touches across channels, each channel (including email) can be used a bit more sparingly and thoughtfully – which means less risk of over-emailing prospects into annoyance or spam. As a bonus, interacting on LinkedIn or by phone often increases the likelihood that when your email does arrive, the prospect recognizes your name and wants to open it.
  

Deliverability at Scale Case in Point: To illustrate the impact of these practices, consider the approach used by Martal Group, a B2B lead generation agency with omnichannel outreach expertise. Martal’s team has spent 15+ years mastering outbound sales, so they know the pitfalls of scaling poorly. They’ve built an AI-driven sales platform that bakes in deliverability safeguards: it verifies contact data upfront (so you don’t send to bad emails that bounce), automatically warms up new email accounts and rotates sender addresses during campaigns, and even sequences messages across multiple custom domains to protect clients’ primary domains (9). The result is that Martal’s large-scale campaigns maintain high inbox placement and engagement. Clients benefit through higher email deliverability and more efficient campaigns, without having to micromanage the technical details (9). This shows that when you prioritize deliverability from the start, you truly don’t have to sacrifice quality for quantity. You can scale your outreach and keep your sending reputation pristine – but it takes strategy, the right tools, and ongoing vigilance.

AI-Powered Email Deliverability: Boosting Inbox Rates with Automation

One of the biggest game-changers for email deliverability in 2025 is the rise of AI and automation. We’re not just talking about AI generating email copy (though that’s happening too) – we’re talking about AI actively managing the sending process, monitoring reputation, and optimizing every aspect of your campaigns to maximize inbox placement. AI-powered email deliverability tools are becoming a must-have in the modern sales stack. In fact, 81% of marketing teams now use generative AI for email creation, with 85% saying it improves content quality (12). But beyond content, AI can also dramatically improve technical deliverability and sending strategy. Here’s how AI and automation can boost your inbox rates:

• Smart Sending Schedules: AI can analyze recipient engagement patterns and suggest the optimal times and frequencies to send emails. Instead of a static cadence, AI-powered platforms adjust your sending schedule based on what’s working (and what isn’t). For example, if prospects in the fintech industry tend to open emails late at night, the AI might shift your send times later for that segment. Or it might identify that emails mentioning a certain pain point get higher replies, and prompt you to use that angle more (9). By continuously learning from opens, clicks, and replies, an AI system ensures you’re sending when and how it’s most likely to get a response – which in turn keeps engagement high and spam complaints low.
  
• Automated Email Warm-Up & Rotation: Managing warm-up across multiple email accounts is tedious to do manually (imagine sending and replying to yourself from dozens of inboxes). This is where AI shines. AI-powered deliverability services will automatically conduct warm-up activities in the background: sending gradual trickles of emails between accounts, opening and replying to emails to simulate real engagement, and even moving any of your messages that land in spam back to the inbox. Martal’s platform, for instance, has built-in smart email warming technology and automated messaging rotation to maximize deliverability (8). The AI essentially “babysits” your sender reputation – new addresses are ramped up safely, and message sending is rotated such that no single pipeline gets overheated. By the time you start campaigning to real prospects, the system has already done the groundwork to ensure you hit the inbox. This is an example of AI doing something humans can’t easily scale: maintaining a 30-40% reply rate on warm-up emails by auto-generating realistic interactions (a strategy that significantly boosts sender reputation) (6).
  
• Continuous Email List Cleaning and Verification: AI can also automate the health of your contact lists. Gone are the days of periodically scrubbing emails in a spreadsheet; modern AI tools can verify addresses in real-time (identifying which emails are valid, which are risky, which are role-based addresses, etc.) and can even update or remove contacts that show signs of being inactive. For instance, Martal’s AI outreach system verifies contact info so your emails don’t bounce (9) – a critical step because an email that hard-bounces is not only wasted effort, it slightly dents your sender reputation. Some AI systems integrate with mailbox provider feedback loops to auto-suppress anyone who marks an email as spam, ensuring you don’t keep messaging folks who clearly aren’t interested. All this automation means better deliverability without the manual labor – the AI quietly keeps your lists clean and your domain reputation intact.
  
• Content Optimization to Dodge Spam Filters: AI is increasingly being used to analyze email content for spam-triggering elements before you hit send. Think of it like having a built-in compliance coach. It can check: Is your subject line too clickbait-y? Is your text full of spam keywords? Did you forget the unsubscribe link? Some advanced platforms will give each email template a deliverability score, flagging issues that might cause filtering. And AI doesn’t just criticize – it can help rewrite content. For example, if your original email copy had a phrase that commonly triggers spam filters, an AI writing assistant can suggest an alternative phrasing that conveys the same idea but is less likely to raise red flags. (A simple example: suggesting “at no cost” instead of “FREE!!!”). By fine-tuning language and format, AI helps ensure your content isn’t inadvertently sabotaging deliverability. Additionally, AI-driven personalization can make each email more unique, which avoids the “carbon copy” syndrome that sometimes trips bulk spam algorithms.
  
• Adaptive Sending and Throttling: A huge advantage of AI in deliverability is the ability to react immediately to problems. If a particular mailbox provider (say Yahoo) starts deferring your messages, an AI system can detect that pattern in real-time and throttle down sends to Yahoo addresses temporarily, or redistribute sends to other times, then ramp back up once the ISP’s antipathy subsides. Humans often won’t catch onto an issue like that until significant damage is done; AI will notice after a few messages get delayed or bounce with a specific error. Essentially, AI gives you real-time deliverability insights and automatic course-correction. Martal’s AI, for instance, monitors campaign performance across channels and can adjust on the fly – continuously optimizing based on feedback (8). This means if something starts to go wrong (opens dip, bounces spike), the system can pivot before it becomes a full-blown problem.
  

AI + Human = Deliverability Dream Team: It’s worth noting that AI isn’t a magic wand; it works best in tandem with human strategy. The organizations seeing success are combining AI-driven automation with human oversight. For example, Martal leverages an AI-powered outreach platform plus their team of seasoned deliverability experts. The AI handles the heavy lifting – warming up emails, rotating send-outs, tracking engagement patterns – while humans set the strategy and intervene when needed (e.g. crafting the messaging, deciding which prospects to target, etc.). 

This combination has yielded impressive results. Martal’s clients have enjoyed outcomes “beyond industry standards” by blending 15 years of human expertise with agentic AI (8). In concrete terms, Martal has seen 2X higher ROI, nearly 4X higher conversion rates, and 6.6X higher positive reply rates than typical benchmarks by using AI to optimize outreach (9) – and a big part of those gains comes from more emails landing in the inbox where they belong.

To give a real-world example: one AI-driven campaign Martal ran discovered that B2B leads in the healthcare sector were twice as likely to book a meeting, so the AI dynamically shifted focus to that segment. It also identified the best times to reach out to busy hospital administrators, leading to a significantly higher open rate. All the while, the system kept a close eye on technical health (no IP blacklists, no surge in spam complaints). The result was a higher deliverability and response rate than a manually run campaign could achieve (9).

Another example outside of Martal: Wishpond, a marketing solutions provider, improved their email deliverability scores by 10–25% after integrating an AI-powered warm-up tool (7). This allowed them to increase their outbound email volume without email health issues – they maintained strong inbox placement as they scaled (7). This kind of improvement simply by deploying AI to manage warm-up and reputation shows the potential.

In summary, AI is becoming your silent partner in the battle for the inbox. It works 24/7, adjusting variables and crunching data points that would overwhelm any human team. For outbound sales teams in 2025, leaning on AI for deliverability tasks is a smart move: you get to focus on selling and strategy, while the algorithms focus on getting your emails delivered and read. As we move on, let’s zero in on two of the most crucial AI-assisted tactics for deliverability – email warm-up and inbox rotation. These are core components of the 2025 playbook for SDRs.

Email Warm-Up & Inbox Rotation 101: The 2025 Playbook for SDRs

By now, you’ve heard warm-up and rotation mentioned multiple times – because they are absolutely essential to increasing email deliverability in any modern outbound program. If you’re an SDR or sales leader, mastering these tactics is non-negotiable in 2025. This section will serve as a playbook: breaking down what email warm-up and inbox rotation mean, why they matter, and how to do them right (with or without fancy tools).

What Is Email Warm-Up (and Why It’s Crucial in 2025)?

Email warm-up is the gradual process of building a good sending reputation for a new email account or domain before you use it for large-scale outreach. Think of a new email address like a new phone number: if you start blasting hundreds of people out of the blue, email providers get suspicious. They might ask, “Who is this sender, and why did they suddenly send 500 emails today?” Warm-up avoids that scenario by introducing your email address slowly and organically to the email ecosystem.

Here’s how a typical warm-up works in 2025:

• Start Small: In the first days, send only a handful of emails (say 10–20) per day from the new account (6). These should not be cold sales emails to strangers. Ideally, they are messages to friendly contacts or even just other internal accounts that will interact with them. The goal is to generate normal-looking email activity.
  
• Gradually Increase Volume: Every few days, raise the daily send count a bit. You might go from 10/day to 20, then 50, then 100+ over a period of 2–4 weeks (6). The key is a slow, steady ramp-up without sudden spikes. This shows email providers that you’re a legitimate user who’s naturally growing their sending, rather than a spammer who just got a new domain to spray-and-pray.
  
• Engage with Replies and Interaction: Warm-up isn’t just about sending – it’s about interaction. If you send out 20 emails and get 0 replies, that’s not great for reputation. So, warm-up emails are often coordinated to ensure they get replies or other positive engagement. For instance, you might arrange for colleagues or friends to reply to your messages, or if you’re using an automated warm-up service, it will have other addresses that auto-reply to you. Aim for at least a 30-40% reply rate during warm-up (6) to signal healthy engagement. Also, if any warm-up email accidentally lands in spam, move it to inbox – providers notice that too (it’s a signal that “recipient” thought it was not spam).
  
• Do the Technical Homework: Before sending that first email, set up your DNS records – SPF, DKIM, and ideally DMARC (6). These email authentication steps are table stakes for deliverability. An inbox provider is much more likely to trust your messages if they can be validated as truly coming from your domain and not forged. Warm-up time is also a good time to practice your sending infrastructure: ensure your email footer has an unsubscribe link or at least your contact info (CAN-SPAM compliance), and that your domain has a proper reputation (no previous owners with bad history). If your domain is brand new, some senders even send a trickle of test emails to big providers (Gmail, Outlook, etc.) and then use the provider’s postmaster tools to see if there were any issues.
  

During warm-up, patience is key. It can be tempting to rush it, but doing so voids the whole point – sending too many emails too soon is one of the most common mistakes that lands new senders in trouble (6). The good news: once you’ve warmed up properly, you can scale more confidently. A warm-up is like a regimen that strengthens your “email muscles” so you can handle heavier lifts later.

Keep in mind that warm-up isn’t a one-time task only for brand new domains. It’s also needed whenever you significantly increase email volume or when you introduce a new mailbox or IP. For instance, if you normally send ~100 emails/day from an account and you want to jump to 300/day, don’t do it overnight – treat it like a mini warm-up, increasing by 50–100 per week and monitoring results. Similarly, if you buy additional domains for your outbound (a common tactic so you’re not sending from your main company domain), each of those domains should be warmed up individually.

The Role of Warm-Up Tools & Automation

Manually warming up one email account by emailing friends is doable. But SDR teams often manage dozens of accounts – which makes manual warm-up impractical. Enter warm-up automation tools (many powered by AI, as discussed). These tools create networks of real-looking email accounts that send messages to each other automatically. They might send a dummy email from your new account to another account in the network, have that account open and “read” the email, perhaps mark it as important, and send a reply like “Thanks for the info!” – all without you lifting a finger. This kind of service runs continuously, slowly ramping up the number of such interactions each day. It effectively establishes your account as a trusted sender through consistent positive engagements.

The 2025 market has several reputable warm-up services; some are standalone, and some are built into sales engagement platforms. Martal Group’s AI platform, for example, has this capability built-in – every new client email address Martal uses for a campaign is automatically enrolled in a warm-up sequence with smart sending cadence and engagement before prospecting starts (8). The platform even moves any stray warm-up emails from spam back to inbox and marks them important, mimicking the behavior of a real user who wants those emails (6). This results in a strong sender reputation once actual outreach begins.

It’s worth noting a subtle point: the warm-up process never truly ends. Even after you’re fully ramped up, you should continue some level of warm-up activity in the background to maintain reputation. Think of it like an exercise routine – you don’t stop exercising once you reach your goal shape; you maintain it. Many tools will keep a trickle of warm-up emails going out and coming in daily (maybe 5-10 interactions a day) just to keep the engagement signals fresh. This is especially important if you have lulls in your regular outreach. If you pause cold emailing for a month (e.g., during the holidays), having ongoing warm-up during that period can prevent your sender reputation from decaying due to inactivity.

Proof it Works: We already cited the Wishpond case – they saw up to a 25% improvement in deliverability after using warm-up lead generation software (6). Here’s another data point: a study by ReturnPath found that sending reputation (which warm-up directly builds) is responsible for ~80-90% of email deliverability. In other words, the biggest factor in whether your emails land in inbox or spam is your reputation score, which is exactly what warm-up is cultivating. So it’s absolutely worth the effort.

What Is Inbox Rotation?

Inbox rotation means using multiple email inboxes or sender identities in tandem to spread out your outreach. Instead of one SDR sending all emails from one address (e.g., [email protected]), that SDR might send from several addresses ([email protected], [email protected], maybe [email protected], etc.), or a team of SDRs shares a pool of sending addresses. The goal is to rotate through different inboxes so that each individual address sends a lower volume and stays “under the radar.”

Rotation can happen at the domain level, user level, or both. Some companies create alternate domains that look similar to their main domain for cold outreach (e.g., if the main domain is AcmeCorp.com, they might send cold emails from AcmeCorp.net or AcmeSales.com). Others keep the same domain but use multiple mailbox aliases or addresses per rep. In either case, the idea is to have, say, 5 addresses sending 50 emails each per day rather than 1 address sending 250 emails. All the emails can funnel replies back to the rep’s main inbox or a centralized system, so management isn’t too difficult.

Why do this? Because it mitigates risk and increases scale simultaneously. If one inbox or domain gets blocklisted or throttled, the others are still fine (and you can replace the affected one while it recuperates). It’s a bit like diversifying your investments – don’t put all your outreach “eggs” in one basket. From a deliverability standpoint, rotating send addresses helps avoid accumulating too many sends, bounces, or complaints on any single sender, which keeps each sender’s metrics within acceptable ranges. For example, Gmail might tolerate 5 spam reports on one address before degrading its reputation, but if you were sending all your volume from one address you might hit those 5 spam reports quickly. If that volume is split into five addresses, each might get 1 complaint – staying below the radar.

Additionally, some spam filters have per-sender volume thresholds (especially on new senders). No more than X emails per hour/day from a new sender is considered normal. By rotating, you adhere to those norms. This is especially critical in the first few weeks of a campaign or when emailing large enterprises. We’ve seen cases where emailing 100 employees of the same Fortune 500 company from one address in one day caused those messages to vanish (likely due to internal security filters). Splitting that across a few addresses on different days got through fine.

Implementing Inbox Rotation: Here are some pointers for doing it effectively:

• Maintain Consistent Identity: If using multiple addresses, you typically still want to use the same sender name (e.g., Jane Doe) so the prospect perceives it as the same person reaching out. It’s just coming from different email sources. This consistency is important for building recognition and trust during a sequence. Make sure the signature, title, etc., are uniform across addresses.
  
• Keep Accounts Warm and Monitored: Every address you rotate in needs to be warmed up and actively monitored. Don’t create 10 burner emails and forget to check some of them – a reply sitting unnoticed in an alternate inbox is a lost opportunity. Many teams set up all rotated addresses to forward responses to a primary inbox or CRM. Martal’s system, for example, manages sequences across multiple domains and aggregates the results so nothing gets missed.
  
• Stagger the Usage: You might designate certain days or campaigns to certain inboxes. For instance, Address A sends emails on M/W/F, Address B on T/Th, etc. Or rotate on a per-sequence basis (sequence 1 uses Address A as the sender for steps 1 and 3, Address B for step 2, etc.). There are various strategies – the key is a randomized but controlled rotation to mimic natural sending patterns. You wouldn’t want a prospect getting an email from Address A in the morning and Address B in the afternoon with the same name – that could confuse them. So plan the rotation in a way that is invisible to the recipient.
  
• Use Dedicated Domains for Cold Outreach: Many companies go as far as using a different domain entirely for cold email (to protect their primary corporate domain’s reputation). If you do this, try to keep it obviously related (so prospects don’t question it). For example, use a subdomain like sales.acmecorp.com or a similar domain like acmecorp.co. And definitely include your brand name in the email body or signature to be transparent. Using alternate domains is a smart strategy because if a cold outreach domain gets a poor reputation, it won’t tarnish emails from your main domain (like your client emails or newsletter). Martal often uses custom domains for sending sequences on behalf of clients, precisely so the client’s main domain stays pristine. This is an advanced form of rotation at the domain level.
  
• Stay Organized: With multiple inboxes, organization is key. Keep track of which accounts are active, which are warming, which might need a rest. Also monitor each one’s reputation (some warm-up tools provide per-inbox reputation dashboards). If one address starts seeing deliverability issues, you can pause it and rely on the others in the meantime.
  

When done right, inbox rotation can significantly increase your outreach capacity without hitting deliverability roadblocks. It’s how savvy teams send thousands of emails per week while keeping per-inbox send counts moderate. It does add complexity, but the payoff is huge for scaling.

The 2025 SDR Deliverability Playbook – Summarized

To wrap up this section, here’s a quick playbook checklist for SDRs and teams aiming to boost deliverability:

1. Authenticate Everything: Set up SPF, DKIM, DMARC on all sending domains. This is a one-time technical setup that pays continuous dividends in trust (6).
   
2. Warm Up New Inboxes and Domains: Never cold-start an email account. Use a 2-4 week warm-up plan with gradually increasing volume and plenty of replies/engagement. Leverage automated warm-up tools or services to simplify this.
   
3. Use Multiple Inboxes/Domains: Don’t put all your volume on one sender. Rotate across several addresses (all representing you/your company). This spreads out risk and volume.
   
4. Send Quality, Targeted Content: Keep emails personalized, concise, and valuable to the reader. Avoid spammy language. High engagement content = high deliverability.
   
5. Mind Your Metrics: Continuously monitor bounce rates (aim <2%), spam complaints (aim for virtually 0%, certainly <0.3% (4)), and opens/clicks. If numbers drift into warning territory, adjust before it becomes a crisis.
   
6. Clean Your Lists: Remove unengaged contacts periodically, verify addresses, and don’t buy lists. It’s better to email 1,000 relevant prospects than 10,000 random ones in terms of deliverability and outcomes.
   
7. Stagger and Pace Sends: Send emails in batches, use send throttling if your tool allows, and schedule sends at various times (not a huge blast all at once). Consistency beats volatility.
   
8. Monitor Blacklists: Every so often, check common email blacklists for your domains/IPs. If you show up on one (e.g., due to a spam trap hit), address it quickly – identify the cause, pause sending, reach out to request delisting once the issue is fixed (2).
   
9. Leverage AI and Tools: Don’t fly blind or manually if you don’t have to. Use deliverability tools (many are built into sales engagement platforms) for warm-up, reputation monitoring, and content scoring. And consider an outsourced SDR company or partner if you lack resources – for example, Martal’s omnichannel services include full deliverability management behind the scenes (9), so their clients’ emails consistently land in inboxes without the clients themselves having to manage the intricacies.
   

By following this playbook, you set yourself up to increase email deliverability rates significantly. Instead of fighting deliverability fires, you’ll be focused on having conversations with the prospects who actually see your emails.

Conclusion: Hitting the Inbox (and Booking Meetings)

Email deliverability can feel technical or daunting, but it boils down to this simple truth: if you respect the inbox, you’ll be rewarded. In 2025, respecting the inbox means sending thoughtful, relevant emails, adhering to best practices, and using tools (and tactics like warm-up and rotation) to play by the rules of today’s email environment. Do that, and you’ll stand out from the spammers and sloppy senders. Your messages will reach more decision-makers, your domain will build a strong reputation, and ultimately your outbound campaigns will produce far better results.

Let’s quickly recap the key takeaways for how to increase email deliverability in 2025 without sacrificing outreach scale:

• Quality Over Quantity: Aim for high engagement. It’s better to send 500 well-targeted, personalized emails that land in inboxes than 5,000 generic ones that mostly go to spam. A smaller list that’s carefully curated will outperform a spray-and-pray blast every time.
  
• Warm Up and Protect Your Sender Reputation: Always warm up new sending addresses or domains gradually. Treat your sender reputation as a precious asset – because it is. Rotate inboxes and use multiple domains if needed to stay in good standing. Think long-term: a healthy domain can be an ongoing pipeline, whereas a burned domain is hard to resurrect.
  
• Embrace AI and Automation: Let technology lighten the load. AI can manage a lot of deliverability factors in the background (from optimal send times to automatic warm-ups and adaptive throttling). It’s like having a deliverability expert on call 24/7, ensuring you hit the inbox more often. The teams leveraging these tools are pulling ahead with higher open and reply rates.
  
• Monitor, Learn, and Adapt: Don’t “set and forget” your campaigns. Keep an eye on performance data and be ready to pause or pivot if you see warning signs. The sooner you catch a deliverability issue, the easier it is to fix. Build a culture of continuous improvement – what you learn from one campaign (e.g., best send time, a subject line that triggers spam) should inform the next.
  

Finally, remember that you don’t have to do it all alone. Managing deliverability at scale can be complex. This is where partnering with experts can pay off. Martal Group, for instance, has spent years perfecting the art and science of outbound prospecting outreach. As a part of their omnichannel lead generation service, Martal handles the heavy lifting of email deliverability optimization – from warming up domains and writing AI-personalized emails, to orchestrating sends across email, LinkedIn, and phone in a balanced cadence  (9). They’ve helped hundreds of B2B companies land more emails in inboxes and convert those touches into sales pipeline.

Ready to boost your inbox placement and outbound results? Martal’s team is here to help. We invite you to book a free consultation with Martal Group. In a no-obligation call, our experts will review your current outreach strategy, identify quick wins to improve your email deliverability, and show how an AI-powered, omnichannel approach can skyrocket your campaign performance. Don’t let deliverability challenges hold your sales team back. Book your free consultation today and let’s turn more of those sent emails into opened emails – and those opens into conversations and customers.

References:

1. GlockApps 
2. Stripo – Email Deliverability Statistics 
3. Mailgun – State of Email Deliverability 2025 
4. BuzzStream – New Bulk Sender Requirements 2024–2025 
5. InboxWP – 21+ Email Deliverability Stats 
6. SmartLead – How to Warm Up a Cold Email List 
7. Wishpond Case Study (Warmup Inbox) 
8. Martal Group – AI Sales Platform 
9. Martal Group – “How to Generate Sales Leads in 2025” 
10. Omnisend 
11. Mailmodo
12. Nonprofit Tech for Good