Is 550 5.7.1 from Gmail permanent?

The reply is a hard rejection for that message, but the condition behind it is not permanent. Senders whose reputation recovers in Postmaster Tools stop seeing it, usually within a week or two of fixing the cause.

Does passing SPF, DKIM and DMARC prevent this?

No. Authentication proves who sent the message; this rejection is about whether Gmail thinks the message is wanted. Fully authenticated spam still gets this code.

Why does the bounce only happen for some recipients?

Gmail weighs each recipient's history with you. Someone who has replied to you before is a much weaker spam signal than an address that has never opened a message from your domain.

550 5.7.1 Our system has detected that this message is likely unsolicited mail

Gmail's spam filter scored the message as spam before it reached a mailbox and rejected it at the SMTP level rather than placing it in the Spam folder. The number after the IP in the brackets is an internal reason code that varies by cause. Authentication may be fine; this is about content and reputation.

What the server replies

550-5.7.1 [203.0.113.10 12] Our system has detected that this message is 550-5.7.1 likely unsolicited mail. To reduce the amount of spam sent to Gmail, 550-5.7.1 this message has been blocked. Please visit 550 5.7.1 https://support.google.com/mail/?p=UnsolicitedMessageError for more information.

Sent by: Gmail
Type: PermanentRetry fails
About: Reputation and blocklists
Enhanced code: 5.7.1

Who sends it

Gmail inbound servers, during DATA, when the filter's confidence is high enough to refuse outright. The same code with the wording "The user or domain that you are sending to (or from) has a policy that prohibited the mail that you sent" means a Workspace admin rule blocked it instead.

Why it happens

The sending IP or domain has a poor or unknown reputation in Google Postmaster Tools, often because of a recent spike in volume.
Recipients have been marking similar mail as spam; Gmail generalises those complaints to the whole stream.
The message carries patterns Gmail associates with spam: link shorteners, a mismatch between the visible link text and target, image-only bodies, or an unsubscribe link that does not work.
Bulk mail is going out without a one-click List-Unsubscribe header, which Google now requires.
The message was sent to a list that includes spam-trap addresses, which flags the sender.

How to fix it

Check reputation first
Open Google Postmaster Tools for the domain. If IP or domain reputation is "Bad" or "Low", the content hardly matters; reduce volume and remove unengaged recipients until it recovers.
Send a clean test
Send a plain-text message with no links to a Gmail address you own from the same server. If that goes through, the trigger is the content; if it bounces too, it is the IP or domain.
Fix the message
Replace shortened links with full ones on your own domain, make sure every link's text matches its destination, keep a text part alongside the HTML, and add List-Unsubscribe and List-Unsubscribe-Post headers for any bulk send.
Warm up and watch complaints
Keep the spam complaint rate under 0.3 percent and ramp new volume gradually over two to three weeks. Gmail rate-limits and then blocks senders that jump from a few hundred to tens of thousands of messages a day.

Check it yourself

These free tools show the records and connections behind this code for your own domain or server.

Related codes

Sources

Fewer bounces to look up.

Faivelo sends from authenticated, warmed infrastructure, turns permanent bounces into one clean event for your application and keeps the address out of future sends.

Send with Faivelo

Free tier included. No card needed.