After what period of inactivity should an email sending domain be warmed up again?
Michael Ko
Co-founder & CEO, Suped
Published 7 May 2025
Updated 19 Aug 2025
8 min read
The question of when to re-warm an email sending domain after a period of inactivity is a common one, and it's something I encounter frequently. Many factors influence this decision, including past sending volume, the type of content sent, and the specific mailbox providers you're targeting. There isn't a single, universally accepted answer, as each provider (like Gmail and Outlook) assesses sender reputation differently. However, we can establish general guidelines to ensure optimal email deliverability.
The core principle behind re-warming is to rebuild trust with internet service providers (ISPs). When a domain goes quiet, its active sending history fades from the ISPs' memory. A sudden surge in email volume after a long break can trigger spam filters, as it resembles the behavior of spammers trying to exploit new or previously dormant domains. This can lead to your emails being directed to the spam folder, or even being blocked entirely.
Understanding domain reputation is crucial here. It's not just about the technical setup of your domain, but also how ISPs perceive your sending patterns over time. A consistent, positive sending history—characterized by low bounce rates, low complaint rates, and high engagement (opens, clicks)—is the foundation of good reputation. Inactivity erodes this, and that's why re-warming becomes necessary.
General guidelines for re-warming
Generally, if a domain has been inactive for a period exceeding 30 days, you should consider a re-warmup. For domains with very high sending volumes (e.g., millions of emails per month), even a two-week period of complete inactivity can warrant a reduced send volume upon resumption. The longer the inactivity, the more cautious your re-warming approach should be.
Think of it like this: if you stop driving your car for a few months, the engine might need a gentle start before you hit the highway at full speed. Email domains are similar. ISPs monitor sending activity closely, and a sudden spike can look suspicious. This is why even a relatively short break can be problematic if you resume sending at full throttle immediately.
The ideal re-warming period for a dormant domain can range from a few days to several weeks. This depends on factors such as:
Inactivity Duration: Longer breaks require more extensive re-warming.
Past Reputation: If your domain had a stellar reputation, it might recover faster. A history of issues means a more careful re-warmup.
Sending Volume: Higher planned volumes necessitate a more structured and gradual re-warming process.
List Quality: Sending to a highly engaged list helps speed up the process.
The impact of inactivity duration
The duration of inactivity significantly impacts how mailbox providers perceive your domain. While some providers might retain positive historical data for a while, others might quickly decay (or even reset) your domain's sending reputation after just a few weeks of silence. This dynamic nature of reputation means that what worked before might not work if there's been a substantial break.
For instance, if a domain has been completely idle for three months or more, it's often treated by ISPs as if it were a brand new sending domain. This means you might need to undergo a full email domain warmup process, starting with very low volumes and gradually increasing them. This careful approach helps avoid triggering spam filters and getting placed on a blocklist.
Even for shorter periods of inactivity, like 2-4 weeks, a mini-warmup might be beneficial, especially if you plan to send large volumes. The goal is to signal to ISPs that you are a legitimate sender resuming normal, healthy sending practices. You can read more about warming up email domains and why it is important.
Here's a breakdown of how inactivity length generally affects the need for re-warming:
Inactivity Period
Impact on Reputation
Recommended Action
Less than 2 weeks
Minimal impact, reputation largely maintained.
Resume normal sending, monitor engagement.
2 weeks to 1 month
Reputation may begin to decay slightly, especially for high volume senders.
Consider a minor re-warmup, gradually increase volume over a few days.
1 to 3 months
Significant decay, may be seen as a new sender.
Perform a gradual re-warmup over 1-2 weeks, starting with low volumes to engaged users.
More than 3 months
Reputation is likely reset to near zero. Treated as a new domain.
Conduct a full warm-up process, similar to a new domain or IP.
Remember, these are general guidelines. The exact impact can vary based on your domain's previous history, the quality of your recipient list, and how well you adhere to email best practices. Even if your IP address has remained active, the domain's reputation itself is also a critical factor.
Strategic re-warming approaches
When re-warming, the strategy should mirror that of a new domain warm-up, but perhaps with a slightly accelerated schedule if the inactivity period wasn't excessively long. The key is to gradually increase your sending volume, starting with your most engaged subscribers. This helps demonstrate positive sending behavior to ISPs.
Monitor your deliverability metrics closely during this period. Keep an eye on your open rates, click-through rates, bounce rates, and spam complaint rates. If you notice any spikes in bounces or complaints, or a dip in engagement, it's a sign that you might be increasing volume too quickly. In such cases, reduce your sending volume and extend the re-warming period. Tools like Google Postmaster Tools can provide valuable insights into your domain's performance.
Gradual increase of volume
Start with a small volume of highly engaged subscribers, then slowly expand your audience and volume daily or every few days. This applies whether it's a new domain, a new subdomain, or re-warming an inactive domain.
Target engaged recipients
Focus on lists with high open and click rates. Engaged recipients provide positive signals to ISPs, improving your sender reputation. Avoid sending to old or unengaged contacts during this phase.
It's also important to ensure your email authentication records (SPF, DKIM, DMARC) are correctly configured and have remained so throughout the inactivity period. Any issues with these can severely hinder your re-warming efforts and lead to emails landing in the spam folder. Regular monitoring of these records is a non-negotiable best practice for any sender.
Considerations for different sending scenarios
The context of your sending matters. Are you resuming marketing campaigns or transactional emails? Transactional emails often have higher engagement rates and can sometimes warm up a domain more quickly due to their expected nature. Marketing emails, especially if sent to a broad list, might require a more extended and cautious re-warming schedule.
If you're dealing with cold contacts, the re-warming process becomes even more critical and potentially longer. Mailbox providers are increasingly scrutinizing unsolicited emails. Without a strong, active sending history, your chances of reaching the inbox with cold outreach diminish significantly, often leading to bounces or immediate blocklisting (or blacklisting).
High volume, short break
A domain previously sending millions of emails weekly, then goes quiet for 2-3 weeks. The reputation decay might be faster due to the higher volume expectations from ISPs. A sudden return to full volume could trigger alerts.
Low volume, long break
A domain sending a few thousand emails monthly, then becomes inactive for 2-3 months. While the immediate risk might seem lower, the longer period of silence means the domain's reputation will have significantly deteriorated, requiring a more thorough re-warming.
Ultimately, the best approach is to avoid long periods of inactivity. Consistent, healthy sending builds and maintains a positive sender reputation. If inactivity is unavoidable, plan your re-warming strategy carefully, starting small and gradually scaling up. This proactive approach minimizes deliverability risks and helps ensure your emails reach the inbox effectively.
Final thoughts on domain re-warming
Maintaining a continuous, positive sending history is the most effective way to preserve your domain's reputation. This consistency builds trust with mailbox providers, making your emails more likely to land in the inbox.
If a period of inactivity is unavoidable, err on the side of caution and always perform a re-warming. The specific duration of the re-warmup will depend on the length of the break and your previous sending patterns. A general rule of thumb is that if your domain has been dormant for four weeks or more, you should plan for a structured re-warming process to gradually rebuild your sender reputation.
Remember that every email you send contributes to your domain's overall health. By following these guidelines and paying attention to your deliverability metrics, you can maintain a strong sending reputation and ensure your messages consistently reach their intended recipients.
Views from the trenches
Best practices
Maintain consistent sending volumes to preserve domain reputation and avoid being flagged as suspicious.
Segment your list and prioritize sending to your most engaged subscribers during any re-warming phase.
Regularly monitor your email deliverability metrics through Postmaster Tools and DMARC reports.
Ensure all email authentication records (SPF, DKIM, DMARC) are always correctly configured and validated.
Common pitfalls
Resuming full sending volume immediately after a long period of domain inactivity.
Ignoring signs of deliverability issues such as increased bounces or spam complaints during re-warming.
Failing to update or check email authentication records after infrastructure changes.
Sending to unengaged or old lists, which can quickly harm your domain's sender reputation.
Expert tips
A gradual increase in sending volume is crucial, especially if your domain has been inactive for over a month.
For very long periods of inactivity, treat the domain as if it were entirely new infrastructure.
Even if your IP remains active, domain reputation can decay independently, requiring re-warming.
Monitor your engagement rates closely; low engagement can signal the need for a slower re-warming pace.
Marketer view
Marketer from Email Geeks says that the need for a warm-up depends on the volume and whether a shared or dedicated IP is being used. For low-volume campaigns on a shared IP, warm-up may not be necessary.
2019-08-29 - Email Geeks
Expert view
Expert from Email Geeks says that data related to domain reputation can begin to decay after just one week of inactivity. It is advisable not to let a domain remain cold for a month, as after three months of being idle, it will likely be treated as entirely new infrastructure for dynamic reputation purposes.
Outlook) assesses sender reputation differently. However, we can establish general guidelines to ensure optimal email deliverability.
Google Postmaster Tools can provide valuable insights into your domain's performance.
