550 5.7.30: Basic authentication not supported (Microsoft 365)
Your app or device tried to sign in to Microsoft 365 with just a username and password, and Microsoft has turned that off.
Sign-in problem Your app or device couldn't sign in to your own mail server, so the message was never sent. Fix the sign-in settings.
What the bounce message looks like
The wording changes from one provider to another. These are typical examples:
550 5.7.30 Basic authentication is not supported for Client Submission.Common causes
- An older printer, scanner or app that only supports password sign-in
- Microsoft's retirement of Basic authentication for SMTP sending, which turns it off by default from the end of December 2026
How to fix it if you sent the email
- Tell your IT admin and send them the full error.
If you manage the receiving or sending mail system
- Move the app to modern sign-in (OAuth), or send through an SMTP relay connector or a dedicated email service.
- For now, an admin can turn Basic SMTP AUTH back on while you migrate, but plan for its removal.
Free tool: paste the full bounce into the bounce message decoder to get a plain-English reading of every code in it.
Questions people ask
- What does 550 5.7.30 mean?
- Your app or device tried to sign in to Microsoft 365 with just a username and password, and Microsoft has turned that off.
- Is 550 5.7.30 a hard or soft bounce?
- Sign-in problem. Your app or device couldn't sign in to your own mail server, so the message was never sent. Fix the sign-in settings.
- Should I remove the address after a 5.7.30 bounce?
- No. The message never left your own mail server. Fix the sign-in or sender settings and send again.