Why can't I just send to my whole list at once after only sending welcome emails?

Sending your entire list at once after a long period of low volume can trigger spam filters due to the sudden, unusual spike in activity. Mailbox providers interpret this as suspicious behavior, potentially harming your sender reputation and causing emails to be blocked or sent to spam.

How do I define "engaged" if my list has only received welcome emails?

If email engagement (opens, clicks in welcome series) is low, define "engaged" by other means, such as product usage, recent logins, or any other interaction subscribers have had with your brand. Prioritize those who have shown recent interest.

How long should the list warming process take?

The list warming process typically takes anywhere from a few days to several weeks, depending on the size and engagement level of your list, as well as your previous sending patterns. It's a gradual ramp-up, not a quick fix.

What if I don't have product engagement data for my subscribers?

If product engagement data isn't available, focus on the most recent sign-ups in your welcome series who showed any activity. If your list is largely unengaged via email, you might need a more aggressive re-engagement strategy, possibly with a smaller initial send to minimize risk, as discussed in the guide on email list warming .

What should the content of my initial re-engagement emails be?

Initial re-engagement emails should be valuable, remind subscribers of their opt-in, and briefly acknowledge the gap in communication. Focus on providing value, a simple re-introduction, or a special offer to encourage opens and clicks, aiming to turn them into warm leads .

How to warm up an email list after only sending a welcome series? - Sender reputation - Email deliverability - Knowledge base

You've diligently maintained your email list, sending out a thoughtful welcome series to new subscribers. Now, you're ready for a big announcement, perhaps a new product launch or a major update, but suddenly increasing your send volume feels daunting. This is a common situation for many senders who have focused on automated welcome flows.

The challenge lies in your sender reputation. While sending welcome emails builds a baseline level of trust, a sudden jump in volume to your broader list can trigger spam filters at major mailbox providers. These providers are wary of rapid changes, which often characterize the sending patterns of spammers trying to exploit new domains.

Instead of a direct leap into a large campaign, a strategic approach is needed to "warm up" your list. This means gradually reintroducing your full sending volume in a way that signals legitimacy to Internet Service Providers (ISPs), ensuring your important announcement reaches the inbox and avoids getting caught in spam traps.

The impact of sudden volume increases

Mailbox providers, such as

Google and

Yahoo, employ sophisticated machine learning algorithms to detect unusual sending patterns. A sudden spike in email volume from a domain that has previously only sent a low, consistent stream of welcome messages looks inherently suspicious to these systems.

This abrupt change can cause your emails to be flagged as spam, even if your content is legitimate. It signals to filters that something is amiss, potentially harming your sender reputation and impacting overall email deliverability. Maintaining a consistent sending volume, even if small, is key to building trust.

If you're on a shared IP address, which is common with many Email Service Providers (ESPs) like

Mailchimp, a sudden increase in volume and subsequent negative engagement (like spam complaints or low opens) can also negatively affect the reputation of that shared IP. This then impacts other senders using the same IP, which mailbox providers take seriously.

The risk of unchecked volume spikes

Sending a large campaign to an email list that has only received welcome emails for an extended period can severely damage your sender reputation. ISPs view sudden, large increases in sending volume as a potential indicator of spamming activity, leading to emails being diverted to spam folders or outright blocked. This can be especially problematic if you use a shared IP, as it can affect other users.

Strategizing your first major send

The most effective strategy for warming up your list is to segment it based on engagement. Begin by identifying subscribers who have recently opened or clicked links within your welcome series emails. If email engagement is low, consider incorporating data from other sources, such as recent activity within your product or mobile application, as a strong indicator of current interest.

Prioritize sending your initial re-engagement messages to this highly active segment. This approach ensures that your first expanded sends generate positive engagement metrics, which are crucial for building and maintaining trust with mailbox providers. As your reputation strengthens, you can gradually expand your sending to less engaged segments.

It is also highly beneficial to acknowledge the time lapse in your message. A brief, polite note reminding subscribers of their sign-up and explaining the quiet period can preempt spam complaints, helping recipients remember their initial consent. This can significantly improve the reception of your email, as noted in a guide on warming up an email list.

The risky approach

Immediate large send: Deploying a major announcement to your entire list simultaneously, regardless of recent engagement.
High spam risk: This often leads to a spike in spam complaints and unsubscribes from less engaged recipients.
Damaged reputation: Can severely harm your sender reputation, leading to future emails being blocked or sent to spam (also known as a blacklist or blocklist).

The recommended approach

Segment by engagement: Target the most engaged subscribers first, such as recent opens or clicks in your welcome series, or product activity.
Gradual volume increase: Start with a small, active segment and slowly expand sending volume over days or weeks.
Positive engagement signals: Higher open and click rates from engaged users build trust with internet service providers.
Improved deliverability: Helps maintain a strong sender reputation and ensures future campaigns reach the inbox.

Implementing a phased re-engagement strategy

To implement a phased re-engagement, begin by exporting subscribers who interacted with your welcome series emails, such as those who opened or clicked. If that segment is too small, incorporate data from product engagement. For example, if you manage a mobile game, target users who have logged in or engaged with the game recently.

Once you have your highly engaged segment, plan to send a specific "re-introduction" email. This email should be designed to elicit positive responses like opens and clicks, and gently remind them about your brand. You might even include a small, exclusive offer to encourage immediate engagement and signal value.

After sending to this initial group, monitor your deliverability metrics closely. Look at open rates, click-through rates, and critically, spam complaint rates. If these metrics are positive, you can gradually expand your sending to slightly less engaged segments over the next few days or weeks. This controlled ramp-up is crucial for successful warming.

A well-structured warm-up process should be a deliberate, multi-day effort. For comprehensive strategies on how to effectively warm up an email domain, various resources are available to guide you through the process, boosting your deliverability and protecting your sender reputation.

Day	Target Segment	Estimated Volume	Action
Day 1	Welcome Series Engaged (Opens/Clicks)	500-1,000	Send re-introduction email.
Day 2	Product Engaged (Recent Activity)	2,000-5,000	Send re-introduction, monitor metrics.
Day 3-5	Least Active Engaged	5,000-10,000	Send re-introduction, continue monitoring.
Day 6-7	Broad Engaged Segment	10,000-20,000+	Begin sending announcement campaign gradually.

Continuous monitoring and list hygiene

Throughout this warming process, and for all future email sends, continuous monitoring of your email deliverability is non-negotiable. Pay close attention to key metrics such as your open rate, click-through rate, unsubscribe rate, and critically, your spam complaint rate. Tools like Google Postmaster Tools can provide valuable insights into your domain's reputation.

High spam complaint rates or a sudden increase in bounces signal that parts of your list are problematic. Regularly cleaning your list by removing inactive subscribers and hard bounces is essential for maintaining a healthy sender reputation and avoiding email blacklists (or blocklists). This proactive list hygiene prevents future deliverability issues.

Ensuring your email authentication protocols, including SPF, DKIM, and DMARC, are correctly configured is also paramount. These records verify your sending legitimacy and are a fundamental part of maintaining a strong sender reputation, especially when managing changes in your sending volume or cadence.

Example SPF recordDNS

v=spf1 include:_spf.example.com ~all

The long-term benefits

Consistently applying a warming strategy and maintaining strict list hygiene practices builds a robust sender reputation over time. This proactive approach helps your emails consistently land in the inbox, reduces spam complaints, and improves overall campaign performance. Remember, healthy lists lead to healthy deliverability.

Views from the trenches

Best practices

Gradually increase email send volume to warm up your list, as machine learning filters dislike sudden changes.

Target the most recently engaged subscribers first, then progressively expand to less active segments.

Segment based on engagement beyond email, like product usage or activity within your app.

Explicitly mention the quiet period in your message to remind recipients it's a legitimate send.

Monitor deliverability metrics closely, such as open rates, clicks, and spam complaints, after each send.

Common pitfalls

Sending a large, unscheduled blast to an entire list after a long period of inactivity.

Ignoring the impact of sudden volume changes on your sender reputation and shared IP addresses.

Failing to segment your audience, leading to low engagement and high complaint rates.

Not acknowledging the gap in communication, which can lead to higher spam reports.

Neglecting to clean your list of unengaged or bouncing contacts, hurting long-term deliverability.

Expert tips

If using a shared IP, understand that your sending behavior impacts the reputation of other senders on that IP.

Maintain detailed records of your normal daily and weekly send volumes to understand baseline performance.

For product-engaged users, leverage that engagement as a strong signal for initial email outreach.

Consider the entire email infrastructure, including your ESP and IP type, when planning a warm-up.

A multi-day, incremental ramp-up is almost always safer than a single, large send after a quiet period.

Expert view

Expert from Email Geeks says: Machine learning filters dislike change and have observed spammers slowly trickling mail before a large send. Consider your normal daily and weekly send volumes to plan effectively.

2021-05-28 - Email Geeks

Expert view

Expert from Email Geeks says: Consider your email infrastructure, including your Email Service Provider (ESP), whether you use a shared IP, or if you're on a platform like AWS SES.

2021-05-28 - Email Geeks

Establishing long-term email success

Warming up an email list after a period of only sending welcome series emails is a critical step for maintaining good sender reputation and ensuring your important messages reach the inbox. It's a proactive measure that safeguards your email program's long-term health.

A strategic, phased approach, beginning with your most engaged subscribers and gradually increasing volume, is essential. This signals positive sending behavior to mailbox providers and helps avoid being flagged by spam filters or landing on an email blocklist (or blacklist).

By prioritizing consistent engagement, vigilant list hygiene, and careful volume management, you can transition smoothly from a welcome series-only program to a robust, high-volume email marketing strategy, securing long-term deliverability and success.