What 550 5.7.1 means
The message Gmail attaches to this code is “The IP you're using to send email is not authorized to send email directly to our servers.”, 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 5.7.1 says what class of problem it is: reputation. The receiver judged the sending domain or IP untrustworthy on its history. This is the class warming addresses.
Why it happens
The receiver has a history for the sending domain and the IP behind it, and that history is bad enough to refuse mail outright. It is built from what the receiver's own users did with previous mail: marked it as spam, deleted it unread, never opened it, plus how much of it went to addresses that do not exist and how suddenly the volume changed.
What to do first: Sending IP is in a dynamic/PBL range. Send through your provider's SMTP, not direct-to-MX.
Why warming does not fix this
Warming builds sender reputation. 550 5.7.1 in this form is a reputation 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
- Check the domain in the reputation checker (blacklists, auth, age)
- Read the provider's own verdict: Postmaster Tools for Google, SNDS for Microsoft
- Cut the volume, then rebuild the reputation with warming
Related codes
- 550 5.7.1 (Gmail): very low sending domain reputation
- 550 5.7.1 (Microsoft): unable to relay
- 550 5.7.1 (Microsoft): delivery not authorized
- 421 4.7.0 (Gmail): very low reputation, deferred
- 421 4.7.28 (Gmail): unusual rate of unsolicited email
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 5.7.1
What does 550 5.7.1 mean?
Gmail returns 550 5.7.1 with the message "The IP you're using to send email is not authorized to send email directly to our servers.": IP not authorized to send directly. The receiver judged the sending domain or IP untrustworthy on its history. This is the class warming addresses.
Is 550 5.7.1 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 5.7.1?
Sending IP is in a dynamic/PBL range. Send through your provider's SMTP, not direct-to-MX. Gmail's own reference for the code is linked on this page.
Does email warmup fix 550 5.7.1?
No. 550 5.7.1 in this form is a reputation problem, and warming builds reputation, which is not what is failing here. Fix the cause and the bounce stops.