Gmail 501 5.7.11
Syntax error, no parameters allowed
Gmail 501 5.7.11 means: syntax error, no parameters allowed. It is a permanent failure, so do not retry it unchanged. A command that takes no parameters, such as STARTTLS, was sent with some. Fix the client.
Gmail’s exact wording
Quoted from Google Workspace Admin Help: Gmail SMTP errors and codes, checked 2026-11-05. Placeholders are Gmail’s own.
Reply text
Syntax error (no parameters allowed). For more information, go to About SMTP error messages and review RFC 3207 specifications.
| Who sends it | Gmail and Google Workspace |
|---|---|
| Basic code | 501: Syntax error in parameters or arguments (RFC) |
| Enhanced code | 5.7.11: Encryption required for requested authentication mechanism |
| Permanent or temporary | Permanent (5xx) |
| Verifying the list prevents it | No |
In practice
Gmail returns this when a command such as STARTTLS is sent with extra parameters it does not take. It is a client bug, often in hand-written SMTP code, and happens on every attempt until the client is fixed. Standard mail libraries send the command correctly. The recipient address and your reputation are not involved.
What the sender should do
A command that takes no parameters, such as STARTTLS, was sent with some. Fix the client.
Would verifying the list have prevented Gmail 501 5.7.11?
No
This reply is about your sending setup, the message or the receiving system, not about whether the address exists, so verifying the list will not prevent it.
Common questions
- What does Gmail 501 5.7.11 mean?
- Gmail 501 5.7.11 means: syntax error, no parameters allowed. It is a permanent failure, so do not retry it unchanged. A command that takes no parameters, such as STARTTLS, was sent with some. Fix the client.
- Should I retry after Gmail 501 5.7.11?
- No. It is a permanent (5xx) failure, so the same message to the same address will fail again. Fix the cause first. A command that takes no parameters, such as STARTTLS, was sent with some. Fix the client.
- Would verifying my list have prevented Gmail 501 5.7.11?
- No. This reply is about your sending setup, the message or the receiving system, not about whether the address exists, so verifying the list will not prevent it.
Sources
- Google Workspace Admin Help: Gmail SMTP errors and codes (checked 2026-11-05)
- IANA: SMTP Enhanced Status Codes registry (checked 2026-11-05)
- RFC 5321: Simple Mail Transfer Protocol, section 4.2.3 (reply codes) (checked 2026-11-05)
Registry and provider wording is quoted exactly; guidance is written by the SimpleVerifier Team.
SimpleVerifier Team · Last checked against the sources 2026-11-05