We use Amazon Simple Email Service to send all automatic service emails (from no-reply@ourdomain.com) and Google Workspace email for manual emails (from user@ourdomain.com).
We've correctly configured DKIM, DMARK, SPF, etc to AWS SES and Google. We also require TLS.
All emails sent from Google are delivered perfectly to all inboxes. However, when we send emails to any enterprise Microsoft emails, sometimes we're getting the following errors (however, in most cases, emails are not delivered at all without any bounces):
Remote MTA IP: 104.47.18.138
Response Code: 550
Response Status: 5.7.64
Response Message: 550 5.7.64 TenantAttribution; Relay Access Denied [AM7EUR06FT029.eop-eur06.prod.protection.outlook.com ]
After googling this specific error, we see that it's related to incorrect configs of Microsoft products. But we don't use any of Microsoft products.
AWS SES and Microsoft mailing products seem very popular, but it's very weird that there are only a few people who posted the same problems online and didn't get any advice.
