Should email sends be throttled daily or hourly for deliverability and new IP warming?
Michael Ko
Co-founder & CEO, Suped
Published 23 Jul 2025
Updated 18 Aug 2025
8 min read
When launching a new email program or migrating to a new IP address, a common question arises about how to manage sending volume. Should I throttle my email sends on a daily basis, an hourly basis, or both? This decision can significantly impact your email deliverability and how quickly your new IP builds a positive sender reputation. I often see this topic discussed, and there are varying opinions, but I can share what I have observed to be the most effective strategies.
The primary goal of IP warming is to gradually introduce your sending volume to Mailbox Providers (MBPs) so they can observe your sending patterns and recipient engagement. This process helps establish trust. If you send too much too soon, MBPs might interpret it as suspicious behavior, leading to throttling, filtering to spam folders, or even getting your IP address added to a blacklist or blocklist. It's about demonstrating consistent, desired sending behavior over time.
A well-planned IP warming strategy is crucial to ensure your emails reliably reach the inbox. It involves slowly increasing the number of emails sent from a new IP address over a period of weeks or even months. This gradual increase allows MBPs to build a sending history for your IP, associating it with positive engagement metrics rather than sudden, potentially spam-like bursts.
Daily vs. hourly throttling: what matters more
When considering whether to throttle daily or hourly, the consensus among many deliverability professionals leans towards managing daily volume as the primary factor. MBPs largely assess your reputation based on daily sending patterns, looking for consistent growth and positive engagement over a 24-hour period. A sudden jump in daily volume is a much larger red flag than variations within an hour.
While daily thresholds are paramount, hourly throttling can still play a role, especially for very large senders or those with extremely sensitive audiences. Hourly throttling offers finer control, allowing you to react more quickly to potential issues like temporary blocks or deferrals from an MBP. If you notice a spike in deferred messages within an hour, you can pause or slow down your sending to that specific domain, preventing further damage to your reputation. This immediate feedback loop can be invaluable for proactive deliverability management.
However, implementing granular hourly throttling often adds significant complexity to your sending infrastructure. Many Email Service Providers (ESPs) manage daily sending caps as a standard feature, and unless you have a highly specialized sending setup or encounter specific deliverability challenges with smaller, more obscure inbox providers, the added effort of hourly throttling might not yield a proportional return in deliverability improvements. Most large MBPs, like Google or Outlook, are sophisticated enough to understand that email traffic fluctuates throughout the day, as long as the overall daily volume growth is healthy and consistent. They prioritize long-term sender reputation and consistent behavior.
Focus on daily volume
Mailbox Providers primarily monitor your daily sending behavior and volume for reputation building. Gradual increases each day are key.
Simplicity: Easier to implement and manage for most senders and ESPs.
Broad impact: Addresses the main factor MBPs use for reputation assessment, particularly during IP warming.
Hourly throttling (secondary focus)
Useful for very large senders, those with sensitive lists, or for rapid response to real-time delivery issues.
Granular control: Allows for immediate adjustments if deferrals or blocks are detected, potentially mitigating larger issues.
Complexity: Can be harder to set up and monitor, often requiring advanced systems.
Practical considerations for IP warming
When you're warming up a new IP, your main focus should be on establishing a consistent and gradually increasing daily volume. MBPs want to see predictable behavior, not erratic bursts. Starting with a very low volume to your most engaged subscribers and slowly increasing it over days and weeks is a proven approach.
A good IP warming schedule involves doubling your daily send volume every few days, assuming your engagement metrics remain strong. For example, if you send 1,000 emails on day one, you might aim for 2,000 on day three, 4,000 on day five, and so on. This slow and steady growth allows MBPs to build confidence in your sending practices and assign a positive reputation to your new IP address. If you're looking for a comprehensive guide, consider exploring one that outlines specific daily or even hourly send limits. For example, GreenArrow Email provides recommendations for injecting mail into their engine, emphasizing that each day's sending should take at least four hours to avoid being overly aggressive. However, I believe that this particular advice would be highly specific to the particular ESP that you're using. I would ask your ESP what the recommended practice is. If your ESP has an auto-warmup setting, this can be extremely helpful.
Some ESPs, like LuxSci, enable email throttling and gradually increase allowed volumes each night. This can automate much of the warming process, reducing manual effort and potential errors. For transactional emails, the rules are often less strict because these emails are typically triggered by user actions, making it harder to control the exact sending rate. However, even for transactional sends, a sensible approach to new IP usage is still beneficial.
Here's an example of a typical IP warming schedule, though actual volumes and durations may vary based on your sending habits and recipient engagement:
Days
Daily Volume per IP
Notes
1-3
1,000-5,000
Send to most engaged subscribers. Monitor closely.
4-7
5,000-15,000
Gradually increase volume, continue to engaged users.
8-14
15,000-50,000
Expand to broader segments, maintain positive metrics.
15-30+
50,000+
Continue scaling, monitor daily. Aim for consistent sends.
Monitoring and adapting your strategy
Regardless of your throttling strategy, vigilant monitoring is non-negotiable during IP warming and ongoing email operations. You need to keep a close eye on your bounce rates, complaint rates, and deliverability to major MBPs. Tools like Google Postmaster Tools or Salesforce Marketing Cloud's data can provide invaluable insights into your sender reputation and help you identify issues early. Remember that building reputation can take at least 30 days of consistent sending.
If you notice a sudden increase in bounces or a decrease in inbox placement, it's a strong indicator that you might be sending too aggressively or that there are underlying issues with your list quality. In such cases, it’s often wise to temporarily reduce your sending volume (throttle down) to allow your reputation to recover, especially if you get added to a blacklist (or blocklist). Maintaining a healthy email list by regularly removing inactive or invalid addresses is also crucial for long-term deliverability.
Key metrics to monitor
Bounce rates: High bounce rates, particularly hard bounces, indicate poor list quality and can harm your sender reputation.
Complaint rates: Recipients marking your emails as spam will severely damage your reputation. Aim for rates well below 0.1%.
Inbox placement: Regularly test to ensure your emails are landing in the inbox, not the spam folder.
Consistency is paramount throughout the IP warming phase. Erratic sending patterns, with sudden peaks and troughs, can confuse MBPs and hinder your reputation building. Maintaining a steady, predictable increase in volume signals to MBPs that you are a legitimate sender. For some senders, especially those with large or dynamic lists, the concept of staggering email sends can be a valuable technique to spread out the load and maintain consistency.
While daily throttling is generally sufficient for new IP warming, it's essential to understand that hourly limits might still apply by default from some MBPs, especially if they are highly conservative or if your sending behavior triggers their spam filters. For example, a new IP might face a temporary hourly throttle if it sends a sudden burst of emails to a very small set of recipients within a minute. This is less about your warming strategy and more about the immediate reaction of the MBP to unusual sending patterns. In these cases, the MBP usually just defers or soft bounces the emails, and they get sent later automatically. My advice is not to worry about those.
Balancing control and complexity
The choice between daily and hourly throttling is often a balance between effort and granular control. For most email marketers and businesses, focusing on daily volume and a gradual increase during IP warming is the most effective and least complex approach. It aligns with how major Mailbox Providers assess sender reputation. Hourly throttling can offer a safety net for immediate issue detection, but it adds complexity that might not be necessary for everyone.
Ultimately, a successful email program relies on consistent, good sending practices, excellent list hygiene, and continuous monitoring. Throttle your sends in a way that allows you to demonstrate predictable, positive sending behavior to MBPs, and you'll be well on your way to achieving optimal deliverability.
Views from the trenches
Best practices
Start warming a new IP by sending to your most engaged subscribers first, then gradually expand to broader segments.
Aim to double your daily send volume every few days during the initial warming phase if engagement remains high.
Leverage automatic IP warming features provided by your ESP, as they often optimize queuing.
Maintain consistent daily sending volume and avoid drastic fluctuations once your IP is warmed up.
Common pitfalls
Sending a large volume of emails too quickly from a new IP address, which triggers spam filters and reputation issues.
Neglecting to monitor bounce rates, complaint rates, and inbox placement during and after IP warming.
Ignoring soft bounces or deferrals, which can indicate you are hitting temporary hourly limits.
Failing to clean your email list regularly, leading to poor engagement and a higher risk of hitting spam traps.
Expert tips
Focus on daily volume thresholds for warming, as major MBPs primarily assess reputation over a 24-hour period.
Hourly throttling can be beneficial for real-time issue detection, allowing quicker response to deferrals.
For transactional emails, strict warming schedules are less critical due to the nature of triggered sends, but still avoid immediate large bursts.
If your list primarily consists of smaller or more obscure inbox providers, more granular hourly throttling might be worth the added complexity.
Expert view
Expert from Email Geeks says that neither hourly nor daily throttling is solely more important; the key is not sending more mail than an MBP is prepared to accept, and ramping up volume gradually when introducing a new domain or IP tuple.
2024-03-05 - Email Geeks
Expert view
Expert from Email Geeks says that daily volume is probably where senders should look, rather than hourly metrics, for effective IP warming.
Google or 
Outlook, are sophisticated enough to understand that email traffic fluctuates throughout the day, as long as the overall daily volume growth is healthy and consistent. They prioritize long-term sender reputation and consistent behavior.
