451 Server Busy

It appears that microsoft is applying rate limits to SpamTitan currently. If your mail is being deferred with this response: 451 4.7.500 Server busy please follow the below documentation to set up a connector to fix this

Prevent 365 from rate limiting SpamTitan

Please use the below documentation to prevent 365 from rate limiting spamtitan and deferring mail

Steps: 

1.  https://docs.titanhq.com/en/9287-spamtitan-and-office-365-ip-throttling--rate-limits-.html
2.  https://docs.titanhq.com/en/9289-ensuring-your-email-is-not-marked-as-spam-in-office-365.html
3. https://docs.titanhq.com/en/9288-locking-down-your-office-365-mail-server.html
4. If your outbound mail is being deferred please contact microsoft support and request that they add you SpamTitan IP to their "Throttling Exclusion List"