Gmail 553 5.1.3
Recipient address not valid
Gmail 553 5.1.3 means: recipient address not valid. It is a permanent failure, so do not retry it unchanged. The recipient address is not valid RFC 5321 syntax. Correct or remove it.
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 recipient 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 | 5.1.3: Bad destination mailbox address syntax |
| Permanent or temporary | Permanent (5xx) |
| Verifying the list prevents it | Yes, verification catches this |
In practice
Gmail refuses addresses that are not valid under RFC 5321, the SMTP standard, before any message is transferred. Typical causes are missing @ signs, two addresses in one field, spaces inside the address and unescaped special characters. These are found without contacting any server, so a syntax check before sending removes them completely. Gmail rejects these at the RCPT stage, so the message body is never sent. Clean these before importing the list.
What the sender should do
The recipient address is not valid RFC 5321 syntax. Correct or remove it.
Would verifying the list have prevented Gmail 553 5.1.3?
Yes, verification catches this
A mailbox check asks the recipient's server whether the address and domain can receive mail, without sending anything, so the address is flagged before the send instead of bouncing against your domain.
Common questions
- What does Gmail 553 5.1.3 mean?
- Gmail 553 5.1.3 means: recipient address not valid. It is a permanent failure, so do not retry it unchanged. The recipient address is not valid RFC 5321 syntax. Correct or remove it.
- Should I retry after Gmail 553 5.1.3?
- No. It is a permanent (5xx) failure, so the same message to the same address will fail again. Fix the cause first. The recipient address is not valid RFC 5321 syntax. Correct or remove it.
- Would verifying my list have prevented Gmail 553 5.1.3?
- Yes, verification catches this. A mailbox check asks the recipient's server whether the address and domain can receive mail, without sending anything, so the address is flagged before the send instead of bouncing against your domain.
The same code elsewhere
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