Email & SMTP · 1 min read
Resolve RFC 5322 Email Format Errors
What's happening
RFC 5322 is the standard that defines how an email must be formatted. Receiving servers reject messages that break it. Bounce messages look like:
- "The email was rejected because the From header or domain does not meet required technical standards"
- "Message not RFC 5322 compliant"
- "Multiple or missing From headers"
Common causes
- A From name with special characters that aren't quoted properly (for example commas or brackets)
- A From email with a typo, spaces or an invalid domain
- Empty or malformed subject lines
- Custom HTML that adds broken headers
- Reply-To addresses that aren't valid
Fix it
- Check the From name. Remove unusual symbols such as
< > " , ;and emoji. - Check the From email. Make sure it's a complete, valid address on a domain you've verified.
- Add a subject line to every email.
- Check Reply-To. Make sure any reply address is valid.
- Review custom code. If you imported HTML, rebuild the email in the builder or remove any header-like code.
- Send a test email and confirm it arrives.
Tip
Workflow and campaign emails can each have their own sender settings. Fix the From details everywhere the error appears.