Standard SMTP codes · permanent error
534: authentication method too weak
The server refused the login because the authentication method the client chose is weaker than its policy allows for this user.
- Standard
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 534
- 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
534 Authentication mechanism is too weak
What it means
RFC 4954 defines 534, with enhanced code 5.7.9, for an AUTH command whose mechanism is weaker than the server permits for that user, and says the client should retry with a different mechanism. It is a login failure, so no mail leaves through that session. Mail clients that let you pick the method usually offer choices such as normal password, encrypted password and OAuth, and the server lists the ones it accepts after AUTH in its EHLO reply.
Common causes
- A client set to an older or plain method that the server no longer accepts for this account.
- An account policy that requires a stronger method such as OAuth.
How to fix it
- 01Change the client's authentication setting to a method the server offers.
- 02If the provider requires OAuth, use a client or library that supports it.
- 03Check the provider's documentation for its required SMTP settings.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
Related codes
- 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.
- 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.
- 538Encryption required for this login method.The authentication method the client chose is only allowed over an encrypted connection, and this connection is not encrypted.
All 105 standard codesEvery code in the wikiPaste your own bounce