Does batching email sends improve deliverability?

Key findings

1. Limited impact for healthy senders: For email programs with established good sender reputations and moderate volumes (e.g., under a million emails per day per IP), batching emails purely for deliverability might not yield significant benefits. Mailbox providers (ISPs) are sophisticated and can handle large, consistent volumes from trusted senders.
2. Addressing underlying issues: If you are considering batching to improve deliverability, it's often a sign of an underlying issue, such as a damaged sender reputation or an un-warmed IP. Addressing these root causes, perhaps by reviewing your email list quality or sending volumes, is typically more effective than just batching.
3. Warming up: Batching can be a component of an IP warming strategy, gradually increasing send volumes over time to build trust with ISPs. This is a deliberate, temporary tactic, not a permanent solution for ongoing deliverability.
4. Engagement signals: Some strategies involve sending a small, engaged batch first to generate positive engagement signals, which can then positively influence the deliverability of the subsequent, larger sends.

Key considerations

1. Traffic management: Batching is most effective when managing backend systems, such as website traffic or call center capacity, to ensure resources are not overwhelmed by a sudden influx of users responding to an email campaign.
2. Time zone optimization: Sending emails in batches tailored to recipients' local time zones (send time optimization or STO) can improve engagement metrics, which in turn can indirectly support deliverability. This is a strategic marketing decision, not purely a technical deliverability fix.
3. Sender reputation: Maintaining a strong sender reputation through consistent sending practices and high engagement is far more impactful than simple batching for deliverability. Focus on list hygiene, content quality, and authentic engagement to avoid being flagged by spam filters. As Mailchimp explains, major ISPs already batch and postpone delivery internally to prevent spam.
4. List size and composition: For very large lists (millions of daily sends) or lists with a significant proportion of free email accounts (Gmail, Outlook.com), careful sending strategies, which may include some form of rate limiting or batching by your Email Service Provider (ESP), are typically handled automatically by modern ESPs. For smaller lists, batching for reputation benefits is often unnecessary.

Key opinions

1. Tradition vs. Necessity: Many marketers admit that batching is a deeply ingrained tradition for large lists, often without clear current deliverability benefits for healthy sending programs. The belief is that pushing a massive volume of emails at once might negatively impact reputation with free email providers.
2. Website Traffic Management: A common and practical reason for batching is to prevent overwhelming a website or call center with a sudden spike in traffic or inquiries immediately after a large email send, ensuring a smooth customer experience.
3. Engagement-focused Batching: Some marketers proactively batch based on engagement history or local time zones to maximize opens and clicks, indirectly boosting sender reputation through positive recipient interaction. This aligns with Vero's insights on optimizing sends.
4. Scale of Sending: What constitutes a 'large' send that might warrant batching is relative. For many marketers, even sends of several hundred thousand emails are not considered large enough to require manual batching for deliverability, especially if their lists are well-maintained.
5. Segmenting by engagement: Splitting email sends by engagement levels, where highly engaged users receive emails first, is a strategy some marketers use to generate positive signals early, which can help deliverability for the rest of the list.

Key considerations

1. Audience composition: The percentage of free email accounts (like Gmail) versus corporate domains in a list can influence the perceived need for batching, as free accounts often have more aggressive spam filters.
2. Marketing platform capabilities: The capabilities of the Email Service Provider (ESP) or marketing automation platform, such as built-in send time optimization or throttling features, can automate what marketers might otherwise attempt to do manually through batching. For example, some ESPs offer segmentation features.
3. Testing is key: Marketers should test if batching actually provides tangible benefits for their specific sending program, as results can vary based on list quality, sending volume, and IP reputation. What works for one sender may not work for another.
4. Email type: Service emails, especially in industries like travel, often benefit from batching not for deliverability, but to align with customer service capacity, ensuring prompt handling of inquiries that arise from the email send.

Key opinions

1. Unnecessary for most: For healthy marketing programs or typical send volumes (e.g., in the hundreds of thousands or even low millions daily per IP), experts do not recommend routine batching for deliverability purposes. ISPs won't 'notice' or penalize such volumes from good senders.
2. When it helps: Batching can be part of an effective remedy if you are actively addressing a deliverability problem, such as recovering from a poor sender reputation or warming up a new IP address. It should be a temporary measure in such cases, combined with other IP warming strategies.
3. Engagement first: A tactical use of batching involves sending a small, highly engaged segment of your list first (e.g., 15-30 minutes before the main send). This can generate positive engagement signals, which may positively influence how the rest of the campaign is handled by ISPs.
4. Corporate vs. freemail: Corporate email filters typically do not 'care' about the sending speed or batching in the same way consumer-facing freemail providers might. Their filtering decisions are often based on different criteria, making batching less relevant for those domains.
5. Traffic management priority: Experts frequently cite managing website traffic spikes or customer service capacity as valid, non-deliverability related reasons to implement batch sending. This is a practical operational decision rather than a deliverability one.

Key considerations

1. Scale of operations: Companies sending tens of millions of emails daily from a single IP address still use practices that resemble batching or throttling, often managed by their ESPs, to maintain consistency and avoid overwhelming receiving servers. However, this is for volumes vastly larger than typical marketing sends.
2. Temporary measure: If batching is employed to address deliverability issues, it should be temporary. The focus should remain on improving sender reputation and list quality so that normal, un-batched sending can resume once the issues are resolved. This is akin to managing large sends without a fully warmed IP.
3. Underlying issues: Experts stress that batching should not be a crutch for poor list hygiene, low engagement, or other fundamental problems that lead to emails going to the spam or junk folder. These underlying issues must be addressed directly for long-term deliverability success. More on this from SpamResource.
4. ISP throttling: Many ISPs already implement their own forms of throttling and greylisting to manage incoming email volume and identify suspicious patterns. This means ESPs often handle the optimal sending speed on the sender's behalf.

Key findings

1. Server resource management: Documentation frequently points to batching as a method to prevent overwhelming sending servers or the receiving servers of Mailbox Providers (MBPs), ensuring efficient processing and delivery of emails.
2. Spam filter mitigation: Sending emails in smaller, timed batches can improve deliverability rates by making campaigns less likely to be flagged by spam filters, particularly when dealing with sudden, large volumes from unestablished senders. This is a core reason why MailerSend suggests delaying or scheduling email delivery.
3. Gradual reputation building: Batching can be part of a domain or IP warming process, allowing a sender to establish a consistent and positive sending reputation over time rather than attempting to send a massive volume at once.
4. ESP-managed throttling: Many modern ESPs automatically handle the throttling of email sends to various ISPs based on their unique sending limits and reputation policies. This means users typically don't need to manually implement complex batching rules. For example, some ESPs automatically manage dedicated IP sending.

Key considerations

1. Engagement optimization: Some documentation notes that batching, particularly when combined with send time optimization, is used to ensure emails arrive when recipients are most likely to engage, which indirectly benefits deliverability by improving sender reputation metrics.
2. Quota scheduling: For platforms like WordPress with specific email sending plugins, documentation often discusses quota scheduling alongside batching to manage server resources and enhance deliverability, particularly for preventing emails from getting stuck in queues.
3. ISP-specific limits: While not explicitly called 'batching,' ESPs internal processes account for various ISP receiving limits (e.g., messages per hour, connections per IP) which inherently means large campaigns are 'batched' or throttled on the backend to avoid being blocked.