How do I warm up a new email domain or IP?

Warming up means gradually increasing how much email you send from a new domain or IP, so mailbox providers build trust in you over time instead of seeing a cold sender suddenly blast thousands of messages:

• Start small and ramp slowly - begin with a few dozen emails a day to your most engaged recipients, then increase the volume over 4 to 8 weeks.
• Send to your keenest people first - opens and replies from engaged recipients teach providers your mail is wanted.
• Keep it steady - consistent daily sending builds reputation; long gaps then sudden bursts undo the progress.
• Get authentication right before you start - SPF, DKIM and DMARC must be in place from the very first email.

If you send through an established provider on a shared IP, you inherit its warm reputation and barely need to warm up at all.