How to manage large email sending volume spikes for optimal deliverability?
Matthew Whittaker
Co-founder & CTO, Suped
Published 1 Aug 2025
Updated 18 Aug 2025
6 min read
Dealing with unexpected or planned surges in email sending volume is a common challenge for email marketers and deliverability professionals. A sudden spike can alarm mailbox providers (ISPs), potentially triggering spam filters and harming your sender reputation, leading to significant inbox placement issues. It is not recommended to have spikes in sending volume because it signals unusual activity to ISPs.
The key is not to avoid large sends entirely, but to manage them strategically to maintain a healthy sender reputation and ensure your messages reach the inbox. This involves careful planning, technical considerations, and continuous monitoring to adapt to ISP feedback.
Understanding the risks of volume spikes
Large, sudden increases in email volume, especially if they are far beyond your typical sending patterns, can be detrimental to your email deliverability. Mailbox providers like Google and Yahoo monitor sending behavior closely. A significant jump in volume can look like a compromised account or a spammer attempting to blast unwanted messages.
This can lead to your emails being throttled, deferred, or even blocked entirely. Throttling means your emails are sent at a slower rate than you intended, which can delay urgent communications. Deferred emails are temporarily rejected and require your sending system to retry them later, while blocked emails are outright rejected and will not reach the recipient.
A key factor here is the concept of sender reputation, which is built on consistent, positive sending behavior. Volume fluctuations negatively impact this reputation. For more details on this, you can read about how email volume and volume fluctuations affect deliverability. Maintaining a steady sending cadence is crucial for long-term deliverability success, making careful management of volume spikes essential.
Proactive strategies for managing large campaigns
To mitigate the risks associated with volume spikes, proactive planning is paramount. This involves preparing your sending infrastructure and your subscriber list well in advance. Consider your current sending patterns and how much of an increase you anticipate.
One of the most effective strategies is to gradually ramp up your sending volume, known as IP or domain warming. This process builds trust with ISPs by demonstrating a consistent and responsible sending pattern over time. Instead of sending a large volume all at once, distribute the emails over several days or weeks. For example, if your typical volume is 300,000 emails and you plan to send 2 million, a sudden jump will be flagged, but a gradual increase reduces risk.
Mailbox providers generally advise against immediately doubling previously sent volumes, as stated by Salesforce's deliverability readiness guide. If you're planning a campaign that significantly exceeds your usual volume, it’s best to start increasing your sending rate weeks or even months in advance. This approach is outlined by Microsoft's warm-up process, suggesting four to eight weeks for maximum deliverability.
Beyond strategic planning, your email infrastructure plays a vital role in handling large email volumes. Utilizing dedicated IP addresses can provide more control over your sending reputation compared to shared IPs, where your reputation is influenced by other senders. For high-volume senders, dedicated IPs offer a more predictable deliverability path, provided they are warmed up correctly.
Implementing email queues is another critical technical safeguard. Email queues, as highlighted by Mailersend, help manage spikes by processing messages at an optimal rate, preventing your system from attempting to send too many emails too quickly, which would otherwise lead to throttling or blocks from ISPs.
Ensure your email authentication protocols, such as SPF, DKIM, and DMARC, are correctly configured. These protocols verify your sending identity and help ISPs trust your emails. Misconfigurations can lead to deliverability issues, especially when sending at high volumes. Checking your DMARC, SPF, and DKIM records is a foundational step.
Furthermore, maintaining a clean and engaged email list is paramount. High bounce rates, low engagement, and a significant number of spam complaints, even for a single large send, can quickly damage your sender reputation. Regularly cleaning your list by removing inactive or invalid addresses, and focusing on sending to actively engaged subscribers, will support your deliverability efforts during volume spikes.
Dedicated IP vs. Shared IP for Volume Spikes
Reputation Control: Your sending reputation is solely your own, allowing for more predictable deliverability during large campaigns.
Warming Period: Requires a significant warm-up period to build trust with ISPs, especially for high volumes. This is a critical initial step.
Direct Impact: Any issues, like high bounce rates or spam complaints, directly affect your dedicated IP.
Monitoring and adaptation
Effective management of email volume spikes requires continuous monitoring and the ability to adjust your sending strategy in real time. Pay close attention to your deliverability metrics, including bounce rates, complaint rates, and open and click-through rates. These indicators provide valuable feedback on how ISPs and your subscribers are reacting to your sending volume.
Utilize postmaster tools offered by major mailbox providers. Google Postmaster Tools, for example, provides data on your sender reputation, spam rates, and delivery errors, which are crucial for identifying issues early. If you see a sudden increase in bounces or complaints, it's a clear signal to slow down your sending rate.
Be prepared to segment your list further during peak sending times, prioritizing your most engaged subscribers. This ensures that even if you face throttling or blocklisting (or blacklisting) from some providers, your most valuable recipients still receive your emails. Having a strategy for recovering deliverability after a sudden high volume send is also important for unexpected issues.
Understanding Sending Volume Impact
The impact of a volume spike depends heavily on the scale. A jump from 20,000 to 40,000 emails is often negligible to ISPs. However, an increase from 300,000 to 2 million can pose significant risks. This substantial increase is likely to trigger heightened scrutiny from mailbox providers, making it crucial to manage carefully.
Views from the trenches
Best practices
Start with IP warming and gradually increase sending volume over weeks or months, demonstrating responsible sending practices to ISPs.
Segment your audience by engagement, prioritizing active recipients during high-volume sends to maintain positive interaction metrics.
Implement email throttling or queuing mechanisms to control the rate at which emails are sent, preventing overwhelming ISPs.
Regularly clean your email list to remove unengaged subscribers, invalid addresses, and spam traps, reducing bounce and complaint rates.
Maintain consistent sending patterns even outside of peak times to establish and sustain a strong sender reputation with mailbox providers.
Common pitfalls
Sending a sudden, massive burst of emails without prior warming can severely damage sender reputation and trigger spam filters.
Neglecting email list hygiene, which leads to high bounce rates and spam complaints during large campaigns, signaling poor list quality.
Ignoring early warning signs from deliverability metrics, like increased deferrals or soft bounces, which indicates issues are escalating.
Failing to segment lists and sending to an entire inactive audience during spikes, causing low engagement and higher complaint rates.
Not having a plan for managing reputation recovery if a large send goes wrong, leaving the domain vulnerable to ongoing deliverability problems.
Expert tips
Focus on real numbers, not just percentages, when evaluating volume increases, as large numerical jumps are more critical.
Listen carefully to bounce messages and throttling indicators from ISPs to adjust sending speed in real time.
Leverage email queues and scheduling flexibility to spread out large campaigns over an extended period.
During peak sending seasons, be especially wary of changes from major mailbox providers like Yahoo and Outlook, which can impact even small volume increases.
Ensure strong email authentication (SPF, DKIM, DMARC) is in place, as it's foundational for trust, especially at high volumes.
Expert view
Expert from Email Geeks says a sudden spike from 5 million to 10 million emails can definitely cause deliverability problems.
2024-04-03 - Email Geeks
Expert view
Expert from Email Geeks says if you are sending to Yahoo!, increasing volume right now might be problematic due to their recent bulk changes.
2024-04-03 - Email Geeks
Sustaining optimal deliverability
Successfully navigating large email sending volume spikes requires a holistic approach that combines careful planning, robust technical infrastructure, and vigilant monitoring. The goal is to build and maintain a strong sender reputation with ISPs, ensuring that your legitimate emails consistently reach the inbox.
By adhering to best practices like gradual warming, list hygiene, proper authentication, and real-time adjustments, you can effectively manage increased email volumes without compromising your deliverability. This proactive stance will help you achieve your marketing goals while preserving your sender credibility.
