Gmail 503 5.5.1
Bad sequence of commands
Gmail 503 5.5.1 means: bad sequence of commands. It is a permanent failure, so do not retry it unchanged. Commands arrived out of order, for example RCPT before MAIL, or no EHLO first. Fix the order in the sending software.
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
Bad sequence of commands. For more information, go to About SMTP error messages and review RFC 5321 specifications.
Reply text
No DATA after BDAT. An email transaction protocol command was issued out of sequence. For more information, go to About SMTP error messages and review RFC 3030 specifications.
Reply text
EHLO/HELO first. An email transaction protocol command was issued out of sequence. For more information, go to HELO/EHLO email error.
Reply text
An email transaction protocol command was issued out of sequence. For more information, go to About SMTP error messages and review RFC 5321 specifications.
Reply text
RCPT first. An email transaction protocol command was issued out of sequence. For more information, go to About SMTP error messages and review RFC 5321 specifications.
| Who sends it | Gmail and Google Workspace |
|---|---|
| Basic code | 503: Bad sequence of commands (RFC) |
| Enhanced code | 5.5.1: Invalid command |
| Permanent or temporary | Permanent (5xx) |
| Verifying the list prevents it | No |
In practice
Gmail lists five versions of 503 5.5.1, all about commands sent in the wrong order: no DATA after BDAT, MAIL before EHLO or HELO, RCPT missing, and a general out-of-sequence command. These come from scripts and devices with a hand-written SMTP client. A standard mail library or the provider's API avoids them.
What the sender should do
Commands arrived out of order, for example RCPT before MAIL, or no EHLO first. Fix the order in the sending software.
Would verifying the list have prevented Gmail 503 5.5.1?
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 503 5.5.1 mean?
- Gmail 503 5.5.1 means: bad sequence of commands. It is a permanent failure, so do not retry it unchanged. Commands arrived out of order, for example RCPT before MAIL, or no EHLO first. Fix the order in the sending software.
- Should I retry after Gmail 503 5.5.1?
- No. It is a permanent (5xx) failure, so the same message to the same address will fail again. Fix the cause first. Commands arrived out of order, for example RCPT before MAIL, or no EHLO first. Fix the order in the sending software.
- Would verifying my list have prevented Gmail 503 5.5.1?
- 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