Forum Discussion
Remote Server returned '550 5.7.501 Access denied, spam abuse detected.
Also found list of NDR Codes from O365
https://support.office.com/en-gb/article/Email-non-delivery-reports-in-Office-365-51daa6b9-2e35-49c4-a0c9-df85bf8533c3
5.7.501 | Access denied, spam abuse detected | The sending account has been banned due to detected spam activity. | For details, see https://support.office.com/en-gb/article/Fix-email-delivery-issues-for-error-code-451-57500699-ASxxx-in-Office-365-51356082-9fef-4639-a18a-fc7c5beae0c8. Verify that any account issues have been resolved, and reset its credentials. To restore this account’s ability to send mail, contact support through your regular channel. |
https://support.office.com/en-gb/article/Fix-email-delivery-issues-for-error-code-451-5-7-500-699-ASxxx-in-Office-365-51356082-9fef-4639-a18a-fc7c5beae0c8
MicrosoftWhen sending from the onmicrosoft.com domain the cause of the NDR is most likely not that "The sending account has been banned due to detected spam activity."
As I said before, sending from the onmicrosoft.com domain is blocked when the originating IP is part of specific IP classes as a measure of preventing spammers to create free trial tenants and sending spam using them :)