535 5.7.8: login failed: invalid credentials
The SMTP server rejected the login because the username, password or token was wrong or not sufficient, so it will not accept mail from this session.
- Standard
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 535 5.7.8
- Provider
- Standard SMTP codes
- Temporary or permanent
- PermanentRefused for good: the message comes back to the sender, and resending it gets the same answer.
- Who has to act
- The sender. The fix is on the sending side: your domain, your server or your list.
- What the server says
535 5.7.8 Authentication credentials invalid
What it means
RFC 4954 defines 535 5.7.8 as the reply to a failed AUTH command when the credentials are invalid or insufficient, and says the client should ask the user for new ones. It happens at login, before a message is sent, which is why it usually surfaces as a mail client asking for the password again, or as an error in an application's logs. Common reasons are a changed or mistyped password, an account that needs an app password or OAuth instead of its normal password, and providers that have switched off password login for SMTP. RFC 4468 once used 554 5.7.8 for a missing trust relationship, a case that now has its own code, 5.7.14.
Common causes
- A wrong, expired or recently changed password.
- An account with two-step verification that needs an app password or OAuth for SMTP.
- A provider that no longer accepts plain password login for SMTP.
- The wrong username, such as a display name instead of the full email address.
How to fix it
- 01Re-enter the username (usually the full email address) and the password in the client or app.
- 02If the account uses two-step verification, create an app password or switch the client to OAuth.
- 03Check the provider's documentation for the required SMTP server, port and login method.
- 04Sign in to webmail to make sure the account is not locked or disabled.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
Related codes
- 535Authentication credentials invalid.The server rejected the login because the username, password or token is wrong or not sufficient for this account, so no mail is sent.
- 5.7.13User account disabled.The login itself worked, but the account has been disabled by its administrator, so the server will not accept mail from it until it is re-enabled.
- 534 5.7.9Authentication method too weak.The server refused the login because the chosen authentication method is weaker than its policy allows for this user; the client should pick a stronger one.
- 5.7.14Trust relationship required.The submission server needs a configured trust relationship with another server to fetch the message content, and none is in place.
5.7.8 at other providers
- 535 5.7.8Username and password not accepted.Google rejected the user name and password your client used to sign in to its SMTP server, so it will not send mail for it.
- 535 5.7.8Authentication failed for an external address.Fastmail could not sign in to the outgoing server of an external address you send from, most often because its stored password has changed.
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