Email provider · 5.x.x permanent failure
Every SMTP 554 response on record from Zoho (zoho.com), with the verbatim text, the enhanced status code, a severity rating and a plain-English fix.
The transaction failed with no more specific reason offered. In practice the receiver is saying the message is unwanted: a spam verdict, a blocklisted IP, or a policy rejection. The accompanying text is where the detail is.
smtp;554 5.2.3 MailPolicy violation Error delivering to mailboxes,mx.zoho.com
The receiver refused the message for good and points at a mailbox problem (missing, disabled, or full) (enhanced status 5.2.3). Use the wording above to pin down the exact fix.
Provider documentation
smtp;554 5.7.1 Email cannot be delivered. Reason: Email flagged as Spam.
The receiver refused the message for good and points at a policy or security problem (enhanced status 5.7.1). Use the wording above to pin down the exact fix.
Provider documentation
Postmaster & documentation
The transaction failed with no more specific reason offered. In practice the receiver is saying the message is unwanted: a spam verdict, a blocklisted IP, or a policy rejection. The accompanying text is where the detail is. At Zoho, 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 Zoho's postmaster documentation.
