How to manage inconsistent bulk email sending volume during IP warm-up?
Michael Ko
Co-founder & CEO, Suped
Published 21 Apr 2025
Updated 18 Aug 2025
6 min read
Managing inconsistent bulk email sending volume during an IP warm-up can feel like walking a tightrope. On one hand, you need to establish a consistent sending pattern to build a positive sender reputation with Internet Service Providers (ISPs). On the other hand, real-world marketing cycles or business needs don't always align with a perfectly smooth, escalating volume.
I've seen many senders grapple with this challenge. The key is understanding how ISPs perceive your sending behavior and adapting your strategy to mitigate risks, even when your natural sending volume fluctuates. It's about building trust, which is earned through predictable and positive engagement, not just sheer volume.
Why consistent sending volume matters
IP warm-up is the process of gradually increasing the volume of emails sent from a new IP address or one that has been inactive, allowing ISPs to recognize it as a legitimate sender. This incremental ramp-up builds a positive sender reputation. Inconsistent sending volume, especially large spikes or drops, can signal suspicious activity to ISPs, potentially leading to deliverability issues.
For ISPs like Google and Microsoft, consistency is a key indicator of a trustworthy sender. They analyze not only the volume but also the frequency and patterns of your sending. A sudden, large increase in volume after a period of low or no sending can be perceived as a spamming attempt. Similarly, erratic sending can prevent an IP from establishing a stable baseline reputation.
This can result in your emails being throttled, delayed, or even sent directly to the spam folder. In severe cases, your IP address could end up on a blocklist (or blacklist), making it extremely difficult to reach the inbox. Understanding how email blacklists actually work is crucial to avoid these pitfalls. Maintaining a consistent schedule helps ISPs accurately gauge your sending habits and assign a favorable reputation.
Bridging volume gaps with diverse sends
If your primary bulk sends are infrequent, like twice a week campaigns, you might find yourself with gaps in your daily sending volume. This is where strategic planning comes into play. You need to fill these gaps with other types of email traffic to maintain the daily volume your warm-up schedule dictates.
One effective method is to leverage transactional emails or automated flows. These typically have high engagement rates and are often sent daily or multiple times a day. Think welcome emails, password resets, shipping notifications, or price drop alerts. While individually low volume, collectively they can contribute significantly to your daily target.
Another strategy involves segmenting your list more granularly. If you have a large list, you can split your bulk campaigns into smaller, more frequent sends. For example, instead of sending 45k emails twice a week, you could send 25k on Monday, 20k on Tuesday, and then repeat this pattern with different segments on other days to gradually cover your entire list while maintaining daily volume.
Inconsistent sending
ISP perception: Erratic volume can trigger spam filters and damage your sender reputation.
Deliverability impact: Emails may be throttled, delayed, or sent to the spam folder, even with authentication records in place.
Reputation building: It becomes harder to establish a stable and trusted sending history.
Content strategy and list segmentation
A common hurdle is a lack of unique content for daily sends, especially if your team is used to a less frequent schedule. This requires a shift in content strategy during the warm-up period. You might need to generate more diverse content, even if it's smaller, bite-sized pieces, to maintain your volume.
Consider repurposing existing content. If you have a longer email creative, break it down into smaller, focused emails highlighting key features or sections. You can also remail to unengaged segments (those who didn't open or click a previous email), but be sure to change the subject line and provide a new hook to avoid subscriber fatigue. This helps maintain engagement while increasing volume.
Focus on high-engagement segments of your list during warm-up. Sending to your most active subscribers first helps generate positive engagement signals, which are vital for building a good sender reputation. As you progress, you can gradually expand to less engaged segments, but always prioritize quality over quantity in the initial phases. You can find more tips on IP warming strategies and email volume scaling.
Dedicated IP
Offers full control over your sender reputation. Ideal for high and consistent sending volumes.
Pros: Reputation is solely yours, better control during warm-up.
Cons: Requires consistent volume to maintain reputation.
Shared IP
Reputation is shared with other senders. Suitable for lower or inconsistent volumes.
Pros: Less strict warm-up requirements, easier for lower volume.
Cons: Reputation can be affected by other senders' practices.
Monitoring and adaptation
Even with the best planning, email deliverability can be unpredictable. This is why continuous monitoring is non-negotiable during and after your IP warm-up. Pay close attention to your sender reputation metrics, including open rates, click-through rates, bounce rates, and spam complaint rates.
Most email service providers offer dashboards for these metrics. Additionally, utilizing tools like Google Postmaster Tools can provide invaluable insights directly from mailbox providers about your domain and IP reputation. Keep an eye out for any sudden drops in engagement or increases in spam complaints.
If you notice an issue, be prepared to adjust your sending volume downwards temporarily or pause sending to specific problematic ISPs. It's always better to be conservative and protect your reputation than to push through and risk a blocklist. Sometimes, splitting a large send into two smaller sends over consecutive days can help mitigate risk if you're nervous about a sudden volume jump. For a deeper dive into why your emails fail, consult our expert guide.
Example warm-up schedule
This is a simplified example. Actual schedules vary by provider and specific sending habits. Consistent daily sending is generally preferred. For more detailed information, consider resources like SparkPost's warm-up overview and Microsoft's warm-up guide.
Basic IP warm-up schedule (example)plaintext
Day 1-3: 50-200 emails/day
Day 4-7: 200-500 emails/day
Day 8-14: 500-2,000 emails/day
Day 15-21: 2,000-5,000 emails/day
Day 22-30: 5,000-10,000+ emails/day
Final thoughts on managing volume
Managing inconsistent bulk email sending volume during IP warm-up is a common challenge, but it's one that can be navigated successfully with the right approach. It's about maintaining a consistent presence and showing ISPs that your sending behavior is predictable and legitimate, even if your bulk campaigns aren't daily.
By supplementing infrequent bulk sends with regular transactional or automated emails, strategically segmenting your audience, and diligently monitoring your deliverability metrics, you can build and maintain a strong sender reputation. Remember, the goal is long-term deliverability, and patience coupled with proactive management is your best ally.
Views from the trenches
Best practices
Aim for a consistent daily sending volume to establish a strong IP reputation.
Segment your audience to match your warm-up schedule, prioritizing engaged users.
Gradually increase your email volume, avoiding sudden spikes that can trigger filters.
Regularly monitor your deliverability metrics, like open and click rates.
Ensure your email content is engaging and relevant to encourage positive interaction.
Common pitfalls
Stopping warm-up prematurely or having long gaps in sending volume.
Sending high volumes too quickly, leading to blocklists (blacklists) or throttling.
Ignoring engagement metrics, which are crucial for building sender trust.
Sending irrelevant or low-quality content just to maintain volume during warm-up.
Failing to react to early signs of deliverability issues during the warm-up period.
Expert tips
Use a diversified content strategy, including transactional or engagement emails, to maintain volume.
Consider re-engaging non-openers with different subject lines if content allows.
Focus on building reputation with ISPs rather than just hitting numerical targets.
A dedicated IP is preferable for high, consistent volumes, providing more control.
Be prepared to adjust your warm-up schedule based on performance and ISP feedback.
Marketer view
A marketer from Email Geeks says they were worried ISPs would react negatively to inconsistent bulk sends during a volatile warm-up period, especially when their daily volume dropped significantly between large promotional campaigns.
2024-06-05 - Email Geeks
Marketer view
A marketer from Email Geeks highlights that content repurposing, such as breaking down large creatives or remailing to non-clickers with new subject lines, can help maintain consistent sending volume during warm-up.
Google and 
Microsoft, consistency is a key indicator of a trustworthy sender. They analyze not only the volume but also the frequency and patterns of your sending. A sudden, large increase in volume after a period of low or no sending can be perceived as a spamming attempt. Similarly, erratic sending can prevent an IP from establishing a stable baseline reputation.
