Gmail 553 5.1.7
Sender address not valid
Gmail 553 5.1.7 means: sender address not valid. It is a permanent failure, so do not retry it unchanged. Your sender address is not valid RFC 5321 syntax. Fix the From or MAIL FROM in your sending tool.
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
The sender address address is not a valid RFC 5321 address. For more information, go to About SMTP error messages and review RFC 5321 specifications.
| Who sends it | Gmail and Google Workspace |
|---|---|
| Basic code | 553: Requested action not taken: mailbox name not allowed (e.g., mailbox syntax incorrect) (RFC) |
| Enhanced code | 5.1.7: Bad sender's mailbox address syntax |
| Permanent or temporary | Permanent (5xx) |
| Verifying the list prevents it | No |
What the sender should do
Your sender address is not valid RFC 5321 syntax. Fix the From or MAIL FROM in your sending tool.
Would verifying the list have prevented Gmail 553 5.1.7?
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 553 5.1.7 mean?
- Gmail 553 5.1.7 means: sender address not valid. It is a permanent failure, so do not retry it unchanged. Your sender address is not valid RFC 5321 syntax. Fix the From or MAIL FROM in your sending tool.
- Should I retry after Gmail 553 5.1.7?
- No. It is a permanent (5xx) failure, so the same message to the same address will fail again. Fix the cause first. Your sender address is not valid RFC 5321 syntax. Fix the From or MAIL FROM in your sending tool.
- Would verifying my list have prevented Gmail 553 5.1.7?
- 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