Gmail and Google Workspace · permanent error
503 5.7.0: no identity changes permitted
Your client tried to authenticate again in an SMTP session where Gmail had already accepted a sign-in.
- Gmail
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 503 5.7.0
- 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
503 5.7.0 No identity changes permitted.
What it means
RFC 4954 says that once a client has authenticated in a session, the server must reject any further AUTH command with a 503 reply. Gmail does this with these words: the session already has an identity and cannot take another. It shows up when a client sends AUTH twice, for example on a connection reused from a pool, or tries to switch accounts in the middle of a session. To sign in as someone else, open a new connection.
Common causes
- A client that sends AUTH again on a connection where it has already signed in.
- A connection pool that reuses a signed-in connection for a different account.
How to fix it
- 01Authenticate once per connection.
- 02Open a new connection when you need to send as a different account.
- 03Check connection pool settings so connections are not shared between accounts.
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
Related codes
- 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.
- 503Bad sequence of commands.The client sent a command at the wrong point in the conversation, for example message data before any recipient was accepted, or mail before logging in.
- 5.7.0Security or policy refusal, unspecified.The message or session was refused for a security or policy reason that the server did not describe more precisely, or chose not to reveal.
5.7.0 at other providers
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