Gmail delivery response
Gmail 553 5.1.7: The sender address is not a valid RFC 5321 address
Gmail rejected the SMTP sender because its address syntax is invalid. Correct the envelope sender in the application or relay before sending again.
A representative response is:
553 5.1.7 The sender 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 in the envelope sender.
- A display name used where SMTP expects only a mailbox.
- A malformed bounce or return-path address generated by an application.
How to fix it
- Copy the rejected sender address from the SMTP log.
- Correct it in the application, account, or relay configuration.
- Check how the service constructs
MAIL FROM. - Send a new message with the corrected envelope sender.
MailFixIt scope
This is an address-syntax error, not an SPF or DNS error. The MailFixIt checker is not needed for this repair.
Frequently asked questions
What does Gmail 553 5.1.7 mean?
The envelope sender is not valid RFC 5321 address 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.