So a vendor is trying to send one of my domains an email, and they are getting this error:
host xxxxxxxxx-cc.mail.protection.outlook.com [220.127.116.11]
Delay reason: SMTP error from remote mail server after MAIL
451 4.4.4 Temporary server error. Please try again later ATTR5
We are receiving email from other domains just fine. This is the first I've heard of the issue. Anyone have any ideas on what is causing this?