Hi,
I have a very odd issue with exchange online.
Created a 365 online last night, sent a test email shortly after. 550 5.4.1 - rejected. Thought I'd give it an hour, same test same issue. External emails to group not working, internal fine.
This morning, several test 365 groups and user mailboxes - same issue. No external email to new addresses.
- MX records are fine - no changes made
- Mail Flow does not show the rejected messages (only internal successful)
- Barracuda Mail allowing email
Logged with Barracuda initially, they've pointed out it'smail.protection.outlook.com blocking the mail, not them.
Looks to be a DBEB issue - has any one experience troubleshooting this (as opposed to just enabling the relay)? My understanding is that the SMTP address has not been found so the address is rejected - however the addresses appear in AD, AAD and...