Gmail 451 4.3.0
Temporarily rejected
Gmail 451 4.3.0 means: temporarily rejected. It is a temporary failure, so your server retries it. A temporary rejection. Let your server retry. If it says multiple destination domains per transaction are unsupported, send one domain per SMTP transaction.
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
Email server has temporarily rejected this message. Go to About SMTP error messages for more information.
Reply text
Multiple destination domains per transaction is unsupported. Please try again. For more information, go to About SMTP error messages and review RFC 5321 specifications.
| Who sends it | Gmail and Google Workspace |
|---|---|
| Basic code | 451: Requested action aborted: local error in processing (RFC) |
| Enhanced code | 4.3.0: Other or undefined mail system status |
| Permanent or temporary | Temporary (4xx) |
| Verifying the list prevents it | No |
In practice
The second version, multiple destination domains per transaction is unsupported, shows up when a client sends recipients on different domains in one SMTP transaction to a Google server that only handles one. Splitting recipients by domain fixes it. The first version needs no action beyond a retry.
What the sender should do
A temporary rejection. Let your server retry. If it says multiple destination domains per transaction are unsupported, send one domain per SMTP transaction.
Would verifying the list have prevented Gmail 451 4.3.0?
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 451 4.3.0 mean?
- Gmail 451 4.3.0 means: temporarily rejected. It is a temporary failure, so your server retries it. A temporary rejection. Let your server retry. If it says multiple destination domains per transaction are unsupported, send one domain per SMTP transaction.
- Should I retry after Gmail 451 4.3.0?
- Your sending server retries it automatically, because it is a temporary (4xx) failure. Investigate only if it keeps coming back over several hours.
- Would verifying my list have prevented Gmail 451 4.3.0?
- 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.
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