Gmail delivery response
Gmail 553 5.1.3: The recipient address is not a valid RFC 5321 address
Gmail rejected the SMTP recipient because its address syntax is invalid. Correct the address in the envelope or source data before sending again.
A representative response is:
553 5.1.3 The recipient address [email protected] is not a valid RFC 5321 address.
Treat this as permanent until the complete provider response and retry behavior show otherwise.
Common causes
- A missing or extra
@sign. - Spaces, brackets, or punctuation copied with the address.
- A malformed address generated by an application or template.
- A display name sent where SMTP expected only a mailbox.
How to fix it
- Copy the rejected recipient exactly as logged.
- Correct it in the contact record or sending application.
- Check how the application builds the SMTP
RCPT TOcommand. - Send again only to the corrected address.
MailFixIt scope
This is an address-syntax error, not a domain DNS error. The MailFixIt checker is not needed for this repair.
Frequently asked questions
What does Gmail 553 5.1.3 mean?
The SMTP recipient address is not valid RFC 5321 syntax.
Can MailFixIt prove this entire bounce from public DNS?
No. The current checker can evaluate selected public DNS configuration, but it cannot recreate recipient state, credentials, reputation, message content, or a historical provider SMTP decision.
Related email diagnostics
SMTP 5.7.1: Delivery not authorizedSMTP 5.7.1 means delivery is not authorized; use the full response to identify a recipient restriction, relay permission, transport rule, or filtering policy.
Gmail 550 5.7.1: Delivery not authorizedGmail 550 5.7.1 is a broad permanent rejection; match the exact response text to a policy, relay, reputation, header, rate-limit, or IPv6 problem before acting.
Primary sources: Gmail SMTP errors and codes, Google email sender guidelines.