For many years, the advice about sending large email campaigns often included a recommendation to break them into smaller batches. The thought was that by limiting the number of emails sent per hour or per day, we could somehow trick internet service providers (ISPs) into seeing us as less of a threat, or simply manage server load better. It was a common practice, almost a tradition, for lists exceeding a certain size, like 20,000 contacts, to be meticulously batched out over several hours.
The underlying concern was that pushing a massive volume of emails, especially to free email providers like Gmail or Yahoo, could negatively impact sender reputation and lead to emails landing in the spam folder. This fear often led marketing teams to implement throttling measures, even when perhaps unnecessary. It raises an important question: does this old tradition still hold true in today's email landscape?
The reality of email deliverability in 2024 is far more nuanced than simple volume throttling. While batching can play a role in very specific scenarios, it's not a universal fix or a prerequisite for good deliverability for most healthy email programs. Modern inbox providers are sophisticated and look at a wide array of signals beyond just the rate of sending, focusing more on engagement and sender quality. Let's delve into why this is the case.
The true impact of email sending volume
Mailbox providers don't just count the number of emails you send, they evaluate the quality of your sending behavior. This includes factors like user engagement (opens, clicks, replies), complaint rates, bounce rates, and whether your emails are authenticated correctly with DMARC, SPF, and DKIM. For a sender with a strong, positive reputation, sending a large volume of email at once to an engaged list isn't inherently problematic. In fact, many large companies routinely send millions of emails daily from a single IP address without aggressive hourly batching.
Consider the scale some email platforms operate at, sending out promotions to millions of subscribers within a short window. If your list is clean, recipients are engaged, and your email authentication is robust, the total volume alone is unlikely to trigger severe deliverability issues. The primary focus should always be on maintaining a healthy sender reputation by sending relevant emails to an opted-in, active audience.
This means that for most established marketing programs with good list hygiene and consistent engagement, arbitrarily parceling out emails for the sake of it might be an unnecessary step that adds complexity without significant deliverability benefits. Your time and effort are better spent on improving fundamental aspects of your email program that genuinely influence where your emails land, such as email content and list quality.
Why smaller sends don't always need batching
Low volume: For lists under 20,000 or even 400,000, most mailbox providers won't even notice the volume. The impact on sender reputation for these sizes is minimal if the list is healthy.
Corporate vs. freemail: Corporate email filters are often less concerned with sudden volume spikes from known, legitimate senders compared to consumer-facing freemail providers who might be more sensitive to mass unsolicited mail.
Engagement signals: Positive engagement from your subscribers outweighs simple send volume. If your recipients consistently open, click, and reply, your deliverability will remain strong.
When strategic staggering makes sense
While continuous batching isn't a silver bullet for deliverability, there are specific scenarios where strategic staggering or batching can be beneficial. One key area is IP warming when you're starting to send from a new IP address. Gradually increasing your send volume allows ISPs to build a positive reputation for your new IP. Similarly, if you're actively recovering from a damaged sender reputation or a blocklist, a temporary, strategic batching approach can help. This might involve sending a small batch to your most engaged subscribers first, then gradually expanding the send.
Another valid reason for batching emails is less about deliverability and more about operational efficiency. For instance, if you're sending service emails that might prompt a large influx of customer inquiries or website traffic, batching can prevent your call center or website from being overwhelmed. This staggered approach ensures your team can handle the response effectively, leading to a better customer experience.
It's also worth considering send time optimization (STO), which involves sending emails based on an individual recipient's known optimal open times or their local time zone. This isn't strictly batching for volume control, but rather for maximizing engagement, which in turn positively influences deliverability. STO is a far more sophisticated and effective strategy than simply throttling a send over an arbitrary number of hours.
Traditional batching (arbitrary rate limiting)
Motivation: Primarily driven by older beliefs that high volume spikes inherently hurt deliverability, or to manage server load.
Application: Applying a blanket limit (e.g., X emails per hour) regardless of list health or sender reputation.
Effectiveness: Often unnecessary for healthy, engaged lists and can delay campaign completion without significant deliverability gains.
Strategic staggering (intelligent send control)
Motivation: Targeted at specific goals like IP warming, reputation recovery, or managing post-send operational impact.
Application: Using a specific small batch for highly engaged users, or timing sends based on peak engagement times and time zones.
Effectiveness: Highly effective in specific use cases, improving engagement, or mitigating operational risks without being a general requirement for every send.
The dangers of unnecessary batching
Sending emails in batches when it's not truly needed can lead to inefficiencies without delivering significant deliverability improvements. If your list is engaged and your sender reputation is strong, artificially throttling your send volume may simply delay your message reaching recipients, potentially missing optimal engagement windows. It adds a layer of complexity to campaign management that offers little return for healthy sending programs.
The real danger to deliverability comes not from sending a large volume quickly, but from sending a large volume of low-quality or unwanted emails. This batch and blast approach (sending the same message to everyone on your list, regardless of segmentation or relevance) is what truly damages your domain reputation and can lead to being placed on a blacklist (or blocklist). Mailbox providers are increasingly sophisticated at identifying these patterns, regardless of whether you're sending in small hourly chunks or a single large burst.
Focusing on engagement and list quality is paramount. If you're sending to unengaged subscribers, or if your emails are generating a high number of spam complaints or bounces, batching will not solve these fundamental issues. In fact, it might just prolong the problem. The goal is to send emails that recipients want to receive, which naturally leads to better deliverability metrics.
Ultimately, if you're not seeing the inbox placement you expect, the issue is likely rooted in your sender reputation and content quality, rather than simply the speed at which your emails are sent. This is why a comprehensive approach to email deliverability is far more effective than relying on outdated batching practices.
Instead of rigidly applying batching based on volume alone, a more effective strategy for boosting deliverability involves a holistic approach that prioritizes recipient engagement and sender reputation. This means focusing on segmentation, personalization, and sending emails that truly resonate with your audience. Highly targeted emails, even in large volumes, perform better than generic batch and blast campaigns.
Consistent sending patterns over time also contribute significantly to a stable and positive sender reputation. Rather than large, infrequent bursts, maintaining a steady, manageable volume that your recipients expect and engage with is often more beneficial. This helps mailbox providers accurately assess your sending habits and trust your legitimate email flows.
Finally, ensure your email authentication, including DMARC, SPF, and DKIM, is correctly configured. These foundational elements signal to mailbox providers that your emails are legitimate and from an authorized sender. Without proper authentication, even perfectly batched emails might struggle to reach the inbox. Focusing on these core deliverability principles will yield far greater returns than relying on outdated batching techniques.
Views from the trenches
Best practices
Optimize sending times based on recipient engagement history and time zones for better inbox placement and open rates.
If your sender reputation is struggling, consider sending a small, highly engaged batch first to improve initial engagement signals.
Coordinate email send volumes with customer service capacity, especially for transactional emails that might generate inquiries.
Maintain consistent sending patterns rather than sporadic large bursts, as this helps build a stable sender reputation.
Common pitfalls
Batching email lists under 20,000 or even 400,000 contacts, as this is often unnecessary and delays campaign delivery.
Applying arbitrary rate limits (batching) to healthy, engaged marketing programs without a clear deliverability problem.
Assuming that batching alone will resolve underlying issues like poor list quality, high spam complaints, or lack of engagement.
Neglecting fundamental email authentication (SPF, DKIM, DMARC) in favor of simple volume control.
Expert tips
For very large senders (e.g., millions of emails per day), hourly batching is a common practice to manage server load and network throughput, but it's not a universal deliverability requirement for smaller volumes.
Batching can be a temporary strategy when actively recovering a damaged sender reputation or warming up a new IP address, but it should not be a permanent solution.
Corporate email filters are generally less sensitive to large send volumes than freemail providers, especially if the sending domain has a strong, established relationship.
Focus on segmentation and personalization: sending highly relevant emails to specific audience segments is far more impactful for deliverability than general volume throttling.
Expert view
Expert from Email Geeks says that batching is not something they recommend for healthy marketing programs, but it can be one part of an effective remedy if you are addressing a deliverability problem.
2020-03-04 - Email Geeks
Marketer view
Marketer from Email Geeks says that sending emails based on local time zones can be effective to avoid mailing people at inconvenient times, like 6 AM on the West Coast.
2020-03-04 - Email Geeks
Key takeaways for your sending strategy
In summary, while batching email sends was once a common practice rooted in server load management and a cautious approach to ISP throttling, its direct impact on deliverability for healthy, engaged lists is often overstated today. Mailbox providers are far more focused on engagement metrics, sender reputation, and proper email authentication than on raw sending speed for established senders. For small to medium-sized sends (e.g., up to 400,000 emails), traditional batching is largely unnecessary.
However, strategic staggering or batching remains valuable in specific contexts, such as warming up a new IP address, recovering from a damaged reputation, or managing the operational impact of a large send on your customer support or website infrastructure. Ultimately, a strong email deliverability strategy is built on consistent positive engagement, robust authentication, and a deep understanding of your audience, rather than arbitrary volume controls. Focus on these core principles, and your emails are far more likely to reach the inbox.
