Email warmup

Email warmup is the process of building a sending reputation for a new domain or mailbox by sending a small, gradually increasing volume of email that gets opened and replied to before any real outreach goes out.

A new domain has no history, and mailbox providers treat no history as suspicious. If it sends 200 cold emails on day one, most go to spam and the domain starts life with a bad record it may never recover from.

Warmup fixes that by giving the domain a history first. Over two to three weeks, the mailboxes send a handful of emails a day to addresses that open, reply, and move them out of spam, with the daily count rising slowly. By the end, the providers have seen the domain behave like a real sender, and real outreach can start at low volume.

Warmup matters more for prospects on Microsoft 365 than on Google Workspace, because Microsoft is harder on new domains. A program aimed at small businesses, which skew Microsoft, should warm against Microsoft tenants specifically.

An example

An MSP's outreach domains are registered on a Monday. For the next three weeks they send between five and forty emails a day into a warmup network, and nothing goes to a prospect. On day 15 the first real emails go out from the mailboxes that have the longest history, at 20 a day. The others join as they're ready. Nobody skips this step twice.

How long it takes

Two to three weeks before the first real send, and it never fully stops. Most programs keep a trickle of warmup traffic running alongside outreach for the life of the domain.

Related terms

Sending domain · Email deliverability · Domain reputation · SPF, DKIM, and DMARC

If you want this run for you, see our cold email agency, or cold email for MSPs.