Domain warm-up

What it means

M3AAWG explains that a newly registered domain's reputation usually starts as unknown, which filters treat much like bad because there is no history to judge. Domain warming introduces the domain to mailbox providers by increasing volume gradually, which keeps its messages from being flagged only because of a sudden spike. M3AAWG recommends warming a new subdomain too, even when the organisational domain is established.

Its general recommendations: start low and slow (it suggests about 6 weeks as an average), spread messages over the day, send campaigns on a regular schedule, and watch SMTP logs for deferrals and bounces, unsubscribe and complaint spikes, and opens and clicks.

M3AAWG adds that artificial warming practices are not recommended and may be illegal.