Why a new IP address needs a warm-up

Mailbox providers decide quickly whether to trust a sender, and for a brand-new IP address they have nothing to go on. Warm-up is how you give them something.

What providers see

For an unknown IP, providers look at the few signals available: whether authentication passes, whether reverse DNS is sensible, how many messages arrive at once, how many bounce, and whether recipients complain. A new address that suddenly sends a large volume looks the same as one set up to abuse them.

What a ramp does

A ramp starts with low rates and small numbers of connections and raises them day by day. Each step gives the provider more evidence that the traffic is wanted and well formed. If a provider starts deferring, you slow down and let it settle instead of pushing through.

What to do with it

• Fix authentication and reverse DNS before the first message.
• Start with recipients who have recently engaged with you.
• Follow a schedule and write it into your server's per-provider limits instead of relying on discipline.
• Pause when bounces or deferrals spike, find the cause, then continue.

Our warm-up guide describes the built-in schedules and how pausing works.