What 550 5.7.29 means
The message Gmail attaches to this code is “This message was blocked because it wasn't sent over a TLS connection.”, as written on its reference page. The first digit says how final it is: a 5xx reply is permanent for that message, so the sending server gives up and returns a bounce. The enhanced status 5.7.29 says what class of problem it is: configuration. The sending system is misconfigured: relaying through the wrong server, no TLS, no authentication to the outbound server.
Why it happens
The sending system is set up wrong: relaying through a server that will not carry the mail, no authentication to the outbound server, encryption refused, or sending straight to the recipient's server when the provider expects its own. The message never gets far enough for reputation or content to matter.
What to do first: The sending server delivered without TLS. Enable STARTTLS on the outbound server; every major provider offers it.
Why warming does not fix this
Warming builds sender reputation. 550 5.7.29 in this form is a configuration problem, and no amount of engagement history changes it. Fix the cause and the bounce stops; warming is for what comes after, when the mail is accepted and the question becomes which folder it lands in. See how warming works for that part.
How to fix it, in order
- Fix the outbound server: authenticate to it, relay through the right host, enable STARTTLS
- Send through the provider's SMTP rather than direct-to-MX where the error says so
Related codes
- 550 5.7.1 (Microsoft): unable to relay
- 550 5.7.28 (Gmail): unusual rate, blocked
- 550 5.7.1 (Gmail): likely unsolicited email
- 550 5.7.1 (Gmail): rate limited
- 553 5.1.2 (Gmail): recipient domain not found
More on Gmail
- Google Workspace emails going to spam: the Postmaster-led diagnosis, dashboard by dashboard
- Gmail and Yahoo bulk sender requirements: the rules behind Google's authentication and spam-rate rejections
- Google Postmaster Tools domain reputation: what the reputation tiers and the spam rate mean
Questions about 550 5.7.29
What does 550 5.7.29 mean?
Gmail returns 550 5.7.29 with the message "This message was blocked because it wasn't sent over a TLS connection.": not sent over TLS. The sending system is misconfigured: relaying through the wrong server, no TLS, no authentication to the outbound server.
Is 550 5.7.29 a hard bounce or a soft bounce?
A hard bounce for that message: the 550 reply is permanent, and the message is not retried. Whether the address should be removed depends on the cause: here the fix is on the sending side, not the list.
How do I fix 550 5.7.29?
The sending server delivered without TLS. Enable STARTTLS on the outbound server; every major provider offers it. Gmail's own reference for the code is linked on this page.
Does email warmup fix 550 5.7.29?
No. 550 5.7.29 in this form is a configuration problem, and warming builds reputation, which is not what is failing here. Fix the cause and the bounce stops.