535 5.7.8 error: SMTP login failed - wrong username or password
The mail server rejected the credentials used to log in. Nothing about the recipient or content is involved - the message never left your side.
How to fix 535 5.7.8
- Re-enter the username (usually the full email address) and password; check for a trailing space.
- For Gmail and Microsoft accounts with 2-step verification, use an app password.
- If it worked before, the password may have been changed or the account locked.
Why this happens
Something in the server or DNS setup doesn't meet the basic rules of the SMTP conversation: how the server identifies itself, whether it has reverse DNS, whether it uses TLS, or whether it is allowed to relay at all.
How to keep it from coming back
Set a real hostname with matching forward and reverse DNS, enable TLS, authenticate before relaying, and re-test the setup after any change to your mail server or provider.
Should I retry a 535 5.7.8 error?
Not as it stands. A permanent error means the same message will be refused again until the cause is fixed on your side. Fix the cause first, then send a fresh message; if it keeps failing after that, check the full text of the bounce for the exact reason.
Got the full bounce message?
The text after the code names the exact reason, and the same code can mean different things at different receivers. Paste the whole message into the decoder - it runs in your browser and nothing is sent.
Open the bounce decoderRelated error codes
Seeing this again and again? That's usually a reputation or authentication problem we can trace and fix at the source.
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