504 5.7.4: unrecognized authentication type
Your client asked Gmail to sign in with an authentication mechanism that Gmail does not offer, so the sign-in was refused.
- Gmail
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 504 5.7.4
- Provider
- Gmail and Google Workspace
- 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
504 5.7.4 Unrecognized authentication type.
What it means
When a client sends AUTH it names a mechanism, such as PLAIN, LOGIN or XOAUTH2. Gmail refuses a mechanism it does not support with this reply. The mechanisms it accepts appear on the AUTH line of its EHLO response, which on port 587 comes only after STARTTLS; an AUTH sent before STARTTLS gets 530 5.7.0 instead. A client set to an unsupported mechanism such as CRAM-MD5 is the usual case. Google's current table prints this code as 5.7.40; the June 2025 version read 5.7.4, which Gmail's servers still send and this entry uses.
Common causes
- A client set to a mechanism Gmail does not support, such as CRAM-MD5.
- Old software with a fixed list of mechanisms.
- A mistyped mechanism name in a manual or scripted SMTP test.
How to fix it
- 01Set the client to use PLAIN or LOGIN over TLS, or OAuth 2.0 (XOAUTH2) if it supports it.
- 02Check the AUTH line in Gmail's EHLO reply, after STARTTLS, to see which mechanisms it offers.
- 03Update old software whose list of mechanisms does not include one that Gmail accepts.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
- Gmail SMTP errors and codes (Google Workspace Admin Help)knowledge.workspace.google.com
- Gmail SMTP errors and codes, version of June 2025 (Internet Archive copy)web.archive.org
Related codes
- 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.
- 504Command parameter not implemented.The server implements the command, but not the particular parameter or option the client asked for with it.
- 5.7.4Security 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.
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