550 5.7.29 is a permanent SMTP reply meaning gmail: message not sent over tls. Gmail requires bulk senders to use TLS when they deliver mail. Your server connected and sent the message in plain text.
What 550 5.7.29 means
Gmail requires bulk senders to use TLS when they deliver mail. Your server connected and sent the message in plain text.
Common causes
STARTTLS is turned off on your server
Most commonPostfix, Exim or another MTA is not set to use TLS for outbound mail.
The TLS setup fails and the server falls back
CommonAn old TLS version, an expired certificate or a bad cipher list makes the handshake fail.
A device or app sends directly to Gmail
Less commonPrinters, scanners and old apps often cannot use TLS.
How to fix 550 5.7.29
- 1
Turn on opportunistic TLS for outbound mail
In Postfix, set smtp_tls_security_level = may (or encrypt). Other MTAs have the same setting.
- 2
Use TLS 1.2 or newer
Remove old protocol versions and make sure the server certificate is valid and not expired.
- 3
Route old devices through a relay
Send device mail through Google Workspace SMTP relay or your ESP, which use TLS.
Confirm your domain is set up correctly
Most delivery failures — permanent or temporary — trace back to authentication or reputation. Run a free EmailHealth check to confirm SPF, DKIM, DMARC, blacklist status, and TLS are all healthy for your sending domain. If you send in volume, free daily monitoring will alert you before a small issue becomes a flood of bounces.