First, check out Fix Outlook account problems in Office 365.
There you’ll find top solutions to Office 365 email issues, frequently asked questions answered by the Office team, the US support number, and a section where you can email us about your specific problem.
When Office 365 can’t deliver email you sent, you’ll receive an email notification called a non-delivery report. Find your error code for specific help with getting your email delivered:
|Code 4.4.7||Code 5.7.12|
|Code 5.1.10||Code 5.7.124|
|Codes 5.1.1 through 5.1.20||Code 5.7.133|
|Code 5.4.1||Code 5.7.134|
|Codes 5.4.6 through 5.4.20||Codes 5.7.13 or 5.7.135|
|Code 5.6.11||Code 5.7.136|
|Code 5.7.1||Codes 451 5.7.500-699 (ASxxx)|