530 5.7.57: Client not authenticated to send mail (Microsoft 365)
Your app or device tried to send through smtp.office365.com without signing in first.
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:
530 5.7.57 Client not authenticated to send mail. [...]530 5.7.57 SMTP; Client was not authenticated to send anonymous mail during MAIL FROMCommon causes
- "Outgoing server requires authentication" is turned off in the app
- The device is set to send without a username and password
- Port 25 used with smtp.office365.com instead of port 587
How to fix it if you sent the email
- Turn on authentication for the outgoing server and enter your full email address and password (or sign in with Microsoft).
- Use port 587 with STARTTLS. See the Microsoft 365 settings.
If you manage the receiving or sending mail system
- For devices that can't sign in, set up an SMTP relay connector instead.
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 530 5.7.57 mean?
- Your app or device tried to send through smtp.office365.com without signing in first.
- Is 530 5.7.57 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 5.7.57 bounce?
- No. The message never left your own mail server. Fix the sign-in or sender settings and send again.