Email provider · 5.x.x permanent failure
Every SMTP 550 response on record from Yahoo Inc (yahoo.com, aol.com, verizon.net), 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 relaying denied for <[email protected]>
The server will not relay mail for this destination. Send through the correct outbound server for the domain, and confirm the recipient really hosts mail with this provider.
Provider documentation
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 Yahoo Inc, 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 Yahoo Inc's postmaster documentation.
