$ man microsoft-sending-limits

Microsoft: 10-15/day Start, Ramp After Warmed

Microsoft 365 mailboxes should start sending at 10-15 emails per day during warmup. Don't increase volume until the mailbox has been warming for at least 2 weeks and shows healthy engagement metrics.

Microsoft is stricter than Google about cold email. Their spam filters are more aggressive, and new mailboxes have zero reputation. If you start at 25/day on a fresh Microsoft mailbox, you'll trigger spam filters within days. Starting at 10-15 and ramping slowly builds reputation without raising flags. Patience here saves domains.

I configure Microsoft 365 mailboxes in Instantly with a starting limit of 10 emails/day. After 2 weeks of clean warmup (no bounces, healthy open rates in the warming pool), I bump to 15. After another week, 20. I rarely push Microsoft mailboxes past 25/day even when fully warmed. The lower ceiling means I need more Microsoft mailboxes to hit the same volume as Google — that's factored into the infrastructure plan from the start.