Email provider · 5.x.x permanent failure
Every SMTP 550 response on record from Hostpoint, with the verbatim text, the enhanced status code, a severity rating and a plain-English fix.
The mailbox is unavailable and the message is rejected for good. This is the catch-all permanent failure, covering everything from an unknown address to an authentication failure to a reputation block, so the wording after the number is what actually tells you the reason.
smtp;550-SPF-check failed: 550 example.com doesn't allow sending mails from xx.xx.xx.xx (in reply to MAIL FROM command)
The sending IP is not listed in the SPF record for the Return-Path domain. Add every server you send from to that record and wait for DNS to update before resending.
Postmaster & documentation
The mailbox is unavailable and the message is rejected for good. This is the catch-all permanent failure, covering everything from an unknown address to an authentication failure to a reputation block, so the wording after the number is what actually tells you the reason. At Hostpoint, it is a permanent rejection, and the specific reason is in the enhanced status code and message text of each response below.
Match your bounce text to one of the responses below and follow its guidance. Recipient-side wording means fix the address. Authentication or reputation wording (SPF, DKIM, DMARC, blocklist) means fix your sending setup, and check Hostpoint's postmaster documentation.