Email warmup

Gmail and Outlook decide where a message lands based on the reputation of the sender. A mailbox that has never sent anything has none, and a mailbox that goes from zero to hundreds a day looks like a spammer, because that is what spammers do.

Warmup is a slow, measured ramp. The mailbox sends real mail to a pool of domains that reply, mark it as not spam, and pull it out of the junk folder. The volume rises on a schedule, and the schedule bends to what the reputation reading says.

We warm for 6 to 8 weeks. The ramp runs roughly 10, 20, 35, 50 and then 60 messages a day per mailbox. A healthy mailbox settles around 60, and the cap moves with the reading, up and down.

The warmup runs on warming.email, which is our own product. It prepares a domain and hands back one clear number: how much this mailbox can send today. Warmup is the second of the seven stages of outbound engineering; the rest of the system is what keeps the reputation once it is earned.