Should I segment my list during warmup?

Here's the short answer: yes, absolutely. But the why matters as much as the how.

When you're warming up a new IP or domain, inbox providers like Gmail and Outlook are watching your early sends very closely. They have no history with you yet, so they look at engagement signals to decide whether you're a sender worth trusting. Opens, clicks, and replies tell them good things. Spam complaints and ignored emails do the opposite. During warmup, those first signals carry a lot of weight.

If you blast your whole list at once, including the people who haven't opened anything in eight months, you'll mix weak engagement with strong engagement right at the start. That muddy signal can slow your reputation building or, worse, trigger filtering before you've had a chance to establish yourself.

So the fix is simple: start with your best people and work outward from there.

Tier 1: Start here (day 1 of warmup)

• Opened or clicked in the last 30 days
• New subscribers from the last 90 days
• Anyone you'd call a known fan (frequent openers, buyers, responders)

These are the people most likely to engage quickly. That early positive signal is the whole point.

Tier 2: Add once momentum builds (week 2-3)

• Opened or clicked in the last 60 to 90 days
• Moderate engagement, nothing alarming in their history

By now your reputation has some runway. Adding moderately engaged subscribers won't drag down the signal you've been building.

Tier 3: Expand gradually (later warmup stages)

• Last opened 3 to 6 months ago
• Engaged historically, just not recently

Worth including, but worth watching. Track complaints and unsubscribes carefully as you add this group.

Caution tier: Handle with care

• No engagement in more than 6 months
• Unknown engagement history
• Imported contacts you've never mailed before

Honestly, some of these may never belong in a warmup at all. If the engagement history is completely blank, it's worth asking whether those addresses should be validated before you send. Cold or unknown contacts during warmup are one of the most common warmup mistakes people make. (And mistakes at this stage are expensive to undo.)

But one more thing worth saying: the tiers above are a framework, not a formula. Your actual timing should follow your warmup schedule and the engagement signals you're seeing as you go. If complaints are creeping up when you add Tier 3, slow down. If everything looks clean, you can move faster.

If you want a second set of eyes on your list breakdown before you start, our SOS hotline is free. No pitch, just help.