534 5.7.9 error (Gmail): An app-specific password is required
The account has 2-Step Verification on, so a normal password doesn't work for SMTP. The client has to log in with an app password.
How to fix 534 5.7.9
- Create an app password in the Google account's security settings and use it in the SMTP login.
- On Workspace, the admin may need to allow app passwords or use OAuth instead.
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 534 5.7.9 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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