What are warmup best practices recognized by industry bodies?

You've got a new IP, a fresh domain, or maybe you're coming back after a long sending gap. You know you need to warm up. But what does "warming up correctly" actually look like in practice, and how do you know when you're done?

Here's the short version: warmup is about building a track record with mailbox providers before you ask them to trust high volumes. M3AAWG and other industry bodies have published guidance on this for years, and the core principles haven't changed much. Start small, use your best senders, watch the signals, and only increase when the numbers say you can.

Who you send to matters most

During warmup, your subscriber quality is everything. Only send to your most engaged addresses. These are people who opened or clicked in the last 30 to 90 days. Don't mix in old, unengaged contacts or anything from an imported or purchased list. One spam complaint or bounce during warmup can set back your reputation before it's even established.

A realistic volume schedule

There's no single universal table, but the progression that aligns with what industry bodies describe looks roughly like this for a shared or dedicated IP starting from zero:

• Days 1 to 3: 200 to 500 emails per day. Transactional or highly personal content works best here.
• Days 4 to 7: 1,000 to 2,000 emails per day. Watch for soft bounces and complaint signals.
• Week 2: 5,000 to 10,000 emails per day. If engagement stays strong and complaints are near zero, keep going.
• Week 3: 20,000 to 50,000 emails per day. By now you should be seeing consistent open rates and low bounce rates.
• Week 4 and beyond: Scale toward your target volume, doubling roughly every 3 to 5 days as long as metrics hold.

These numbers are guidelines, not laws. A sender with a brand new domain may need to go slower. Someone with an established domain reputation moving to a new IP can sometimes move faster. Watch the signals, not the calendar.

Metrics that tell you to pause

M3AAWG's published guidance, along with feedback loop programs at major mailbox providers, point to a few thresholds that should make you stop and investigate before sending more:

• Spam complaint rate above 0.10% for Gmail traffic, or above 0.30% at Yahoo Mail. Google's own postmaster tools make complaint rates visible in near real time.
• Hard bounce rate above 2%. This signals address quality problems that warmup volume won't fix.
• Soft bounce rate climbing above 8 to 10%. A spike here usually means a mailbox provider is throttling you. Slow down.
• Open rates dropping sharply from day to day. Engagement collapse mid-warmup is a sign your audience segment isn't as fresh as you thought.

If any of these trip, pause volume increases for 48 to 72 hours. Don't go backward unless complaints spike badly. Just hold steady and give the mailbox providers time to recalibrate their view of you.

Consistency matters as much as volume

Industry bodies flag one thing repeatedly: irregular sending during warmup is almost as damaging as sending too fast. If you send 5,000 emails on a Monday and then nothing for four days, the positive engagement signals decay. Sending velocity should be steady and predictable, not bursty. Even if that means sending smaller daily batches, the consistency will build reputation faster than occasional large sends.

When is warmup actually finished?

Warmup is done when your metrics stay stable at your target volume for at least two full weeks. That means complaint rates under threshold, bounce rates under control, and open rates consistent with your historical benchmarks. At that point, you're no longer building reputation. You're operating on it. The distinction matters because ISPs treat a stable sending pattern very differently from an erratic one, even after warmup ends.

But if you're not sure whether your current setup is warmed up correctly, our free Blocklist Checker can show you whether your IP or domain has already picked up a reputation problem. And if things are moving sideways fast, the SOS hotline is free to use.