How email warmup works, and why it takes weeks

Mailbox providers decide where an email lands by looking at the sender's track record: how often its emails get opened, replied to, marked as spam or bounced. A brand-new mailbox has no track record at all.

To a provider, a new mailbox that sends a hundred cold emails on its first day looks exactly like a spammer who just set up an account. Warmup is how a mailbox earns a history before it sends real volume.

What warmup does

Warmup sends a small number of ordinary emails between the new mailbox and a network of real, established mailboxes. Those mailboxes open the emails, reply to them, and move them out of spam when they land there.

Every one of those actions is a positive signal. Day by day, the provider sees a mailbox that sends normal email that people want. The volume grows gradually, so the history looks like a real person settling into a new address.

How long it takes

Plan 2 to 4 weeks of warmup before the first cold email, then ramp cold volume up over the following weeks instead of starting at full speed.

The numbers in the example are per mailbox, per day. Cold volume climbs toward 30 to 50 a day, the range that keeps a mailbox healthy. More volume comes from more mailboxes, not from pushing one mailbox harder.

Keep warming after cold email starts

Warmup doesn't stop when cold sending begins. Cold email draws fewer replies than warmup email, and some recipients will mark it as spam. Warmup running alongside keeps a steady supply of positive signals, so one hard week doesn't drag the mailbox's reputation down.

How to tell a mailbox is ready

• Its warmup emails land in the inbox, not spam, day after day.
• It has been sending consistently for at least two weeks, with no sudden jumps.
• Its domain passes SPF, DKIM and DMARC.

If warmup emails start landing in spam, hold cold volume where it is, or lower it, until placement recovers.

Warmup can't fix bad sending

Warmup builds a history. Bad sending spends it. A list full of invalid addresses, a burst of volume, or emails that draw complaints will undo weeks of warmup in days. Keep lists verified, volume within limits and every email written for the person who gets it.

How Leadgenerator.io handles it

Every mailbox Leadgenerator.io creates starts warming up as soon as its domain verifies, with no setup on your side. Warmup keeps running in the background after the mailbox starts sending, and each mailbox shows its warmup status, so you can see which ones are still warming and which are active.