Email provider · 4.x.x transient failure
Every SMTP 450 response on record from Infomaniak, with the verbatim text, the enhanced status code, a severity rating and a plain-English fix.
The requested action did not happen because the mailbox was briefly unavailable, for example locked, busy, or lightly rate limited. The sending server keeps the message queued and retries it.
smtp;450 4.1.8 Sender address rejected: Domain not found (in reply to RCPT TO command))
The receiver deferred the message and points at an addressing problem (the recipient or sender address itself) (enhanced status 4.1.8). Use the wording above to pin down the exact fix.
Postmaster & documentation
The requested action did not happen because the mailbox was briefly unavailable, for example locked, busy, or lightly rate limited. The sending server keeps the message queued and retries it. At Infomaniak, it is a temporary deferral that is retried automatically, 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 Infomaniak's postmaster documentation.
