5.7.4: security feature not supported
The message or session asked for a security feature, such as a form of secure authentication, that the delivery protocol here cannot support.
- Standard
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 5.7.4
- 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
5.7.4 Security features not supported
What it means
RFC 3463 defines X.7.4 for messages carrying security features, its example being secure authentication, that cannot be supported on the delivery protocol. It is useful only as a permanent error, and the registry pairs it with reply code 504 (command parameter not implemented), so the usual form is 504 5.7.4 in reply to a request the server cannot honour. The answer is to use a feature the server does offer, which it lists in its EHLO reply.
Common causes
- A client asked for an authentication or security option the server does not offer.
- A message or command that relies on a security extension the next server lacks.
How to fix it
- 01Read the server's EHLO reply for the security options it supports (AUTH mechanisms, STARTTLS).
- 02Configure your client to use one of those options.
- 03Update the client or library if it insists on an unsupported mechanism.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
Related codes
- 504Command parameter not implemented.The server implements the command, but not the particular parameter or option the client asked for with it.
- 5.7.3Secure format conversion not possible.Delivery needed the message converted from one secure messaging format to another, and that conversion could not be done.
- 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.
- 5.5.4Invalid command arguments.A valid SMTP command was sent with an argument the server does not accept, because the value was out of range or named a feature it does not know.
5.7.4 at other providers
- 504 5.7.4Unrecognized authentication type.Your client asked Gmail to sign in with an authentication mechanism that Gmail does not offer, so the sign-in was refused.
- 504 5.7.4XOAUTH no longer supported.Your client tried to sign in with XOAUTH, Google's old OAuth 1.0 mechanism, which Gmail has retired in favor of XOAUTH2.
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