How to warm up email sending after a break to avoid spam filters?
Michael Ko
Co-founder & CEO, Suped
Published 24 Apr 2025
Updated 16 Aug 2025
7 min read
Email sending can feel like a marathon, not a sprint. You build up your sender reputation over time, carefully increasing volume and monitoring engagement. But what happens when you hit the pause button? Whether it's for a planned maintenance, a business pivot, or an unexpected issue, taking a break from sending emails can have consequences for your deliverability. Many senders find that after even a relatively short period of inactivity, their emails suddenly start landing in the spam folder, even if the content itself is perfectly clean.
This sudden shift can be frustrating, especially when you're sure your list is clean and your messages are valuable. The truth is, mailbox providers (like Gmail and Yahoo) view consistent sending as a sign of a legitimate sender. A sudden cessation, followed by a sudden resumption of volume, can trigger their spam filters because it looks like suspicious behavior.
The good news is that this is a common challenge, and there's a proven solution: re-warming your email sending. Just as you would warm up a new IP address or domain, you need to gradually re-establish trust with mailbox providers after a period of dormancy. This guide will walk you through the steps to effectively warm up your email sending after a break, helping you avoid spam filters and ensure your messages reach the inbox.
Why sender reputation declines after inactivity
When you take a break from email sending, even for a few weeks, your sender reputation can start to decay. Mailbox providers assess your sending patterns, engagement rates, and complaint rates constantly. Inactivity means they have less recent data points to verify your legitimacy. When you suddenly resume sending at your previous volume, it can look like a dormant account or domain has been hijacked, or that you're attempting to send unsolicited bulk mail.
This perceived abnormality can lead to your emails being flagged as suspicious. Mailbox providers are designed to protect their users from spam, and any significant deviation from established sending habits will raise red flags. This is why even with perfectly legitimate content and a clean list, you might find your emails going to spam.
Understanding reputation decay
Mailbox providers maintain detailed sender reputation scores for domains and IP addresses. These scores are dynamic and are heavily influenced by recent sending behavior. A period of inactivity, especially combined with a sudden spike in volume upon resumption, can negatively impact this score, leading to increased spam classifications. This is a common reason why you may need to warm up your domain again after a break.
The structured approach to re-warming
The core principle of warming up email sending is to gradually build trust. Instead of immediately sending your full volume, you start with a small number of emails and slowly increase it over time. This mimics the behavior of a legitimate sender whose list is organically growing, rather than a spambot or a compromised account.
When you restart sending after a break, it's advisable to begin with your most engaged subscribers. These are recipients who are highly likely to open your emails, click links, and even reply. Positive engagement signals like these are crucial for rebuilding your sender reputation and showing mailbox providers that your emails are valued. As trust is re-established, you can then expand to larger segments of your list.
A structured warm-up plan helps avoid triggering spam filters. Starting too fast, even to a legitimate list, can result in blocklisting (or blacklisting). Consider a tiered approach, increasing your daily volume by a small percentage each day, perhaps 10-20%. The exact pace depends on the length of your break and your typical sending volume. You can find more details on this strategy in high-volume warmup guides.
Example progressive warm-up schedule
Day 1-3: 50-100 emails per day
Day 4-6: 100-200 emails per day
Day 7-9: 200-400 emails per day
Day 10-12: 400-800 emails per day
...
Continue doubling every 2-3 days until desired volume is reached.
Before warm-up (issues)
Spam folder delivery: Many emails land in recipients' spam or junk folders.
Low engagement: Open rates and click-through rates plummet.
Reputation damage: Sender reputation score with ISPs declines.
Reduced blocklist risk: Lower likelihood of being blocklisted.
Essential components for effective re-engagement
Beyond simply increasing volume, several critical elements contribute to a successful re-warmup. First and foremost, ensure your email list is healthy and engaged. Remove any inactive or bounced addresses. Sending to an unengaged list will only amplify negative signals and make your warm-up harder.
Content quality is another key factor. Even during a warm-up, your emails should be valuable, relevant, and free of spammy trigger words or excessive links. Personalization can also play a role, as it encourages engagement from your recipients. Focus on delivering content your subscribers genuinely want to receive and interact with. This approach helps improve email deliverability and avoid spam filters.
Email authentication protocols are non-negotiable for deliverability. Ensure your SPF, DKIM, and DMARC records are correctly configured and aligned. These records prove that your emails are legitimate and prevent spoofing, which is vital for maintaining sender trust. A break in sending doesn't mean these configurations change, but it's a good opportunity to double-check them. More information on authentication can be found in this simple guide to DMARC, SPF, and DKIM.
Content creation for warm-up
Relevance is key: Ensure your content is highly relevant to the initial, most engaged segment of your audience.
Avoid spam triggers: Steer clear of excessive capitalization, exclamation marks, and common spammy phrases.
Clear calls to action: Encourage opens and clicks, which are positive engagement signals.
Plain text option: Provide a plain text version for accessibility and to cater to different email clients.
Protocol
Purpose
Impact on deliverability
SPF
Specifies which mail servers are authorized to send emails on behalf of your domain.
Helps prevent spammers from forging your sender address.
DKIM
Adds a digital signature to your emails, allowing recipients to verify the message wasn't altered in transit.
Ensures message integrity and authenticity, building recipient trust.
DMARC
Uses SPF and DKIM to determine if an email is legitimate and specifies how mailbox providers should handle unauthenticated mail.
Provides reporting and policy enforcement, giving you control over how your domain is used.
Tracking progress and addressing challenges
Monitoring your progress is as crucial as the warm-up itself. Utilize tools like Google Postmaster Tools to keep an eye on your sender reputation, spam complaint rates, and deliverability errors. These insights will tell you if your warm-up strategy is working or if you need to adjust your pace. For example, if you see a spike in spam complaints, it's a clear signal to slow down your sending volume.
Pay close attention to bounce rates. High bounce rates, especially hard bounces, can severely damage your sender reputation. Ensure your list is regularly cleaned to remove invalid or defunct email addresses. Implement feedback loops (FBLs) with major mailbox providers. These will notify you when recipients mark your emails as spam, allowing you to remove those addresses from your list promptly.
Being listed on an email blocklist (or blacklist) is a strong indicator of deliverability problems. Regularly check if your IP address or domain has been added to any public or private blocklists. If you find yourself on a blocklist, investigate the cause and take immediate action to request delisting. Proactive blocklist checking can prevent more severe deliverability issues.
Views from the trenches
Best practices
Always maintain a clean and engaged email list, removing inactive subscribers regularly.
Segment your audience and send relevant content to maximize engagement during warm-up.
Ensure all email authentication records (SPF, DKIM, DMARC) are correctly configured.
Monitor your sender reputation and deliverability metrics using tools like Google Postmaster Tools.
Common pitfalls
Resuming sending at full volume immediately after a break, triggering spam filters.
Ignoring high bounce rates or spam complaints during the warm-up period.
Sending unengaging or generic content, leading to negative recipient feedback.
Failing to monitor blocklists (or blacklists) and address potential listings promptly.
Expert tips
If your content and list are optimal, a gradual re-introduction of email volume to major mailbox providers is crucial.
Before re-warming, conduct thorough testing with internal seeds and third-party services to identify hidden issues.
Review your Google Postmaster Tools data for any changes in reputation, errors, or authentication status.
Implement a slow and steady ramp-up, doubling volume every few days instead of large jumps.
Marketer view
Marketer from Email Geeks says they stopped mailing for 20 days and emails are now going to spam, despite clean content. They are looking for help on whether to warm up from scratch.
2022-09-15 - Email Geeks
Expert view
Expert from Email Geeks says that the quality of the email list is paramount, as even the best content will not perform if recipients did not explicitly request the mail.
2022-09-15 - Email Geeks
Restoring your sending power
Losing email deliverability after a break can be a frustrating experience, but it's a common issue with clear solutions. The key is to understand that mailbox providers prioritize consistent, engaged sending. A sudden re-entry into high-volume sending after a period of dormancy will almost always trigger their spam filters.
By adopting a structured re-warmup strategy, focusing on list hygiene, content quality, and robust email authentication, you can systematically rebuild your sender reputation. Patience and diligent monitoring of your deliverability metrics are your best allies in this process. With a careful approach, you can restore your email sending power and ensure your messages consistently reach your subscribers' inboxes, rather than their spam folders.
