Spam filter · 4.x.x transient failure
Every SMTP 450 response on record from ZeroSpam, 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 4.2.0 <[email protected]>: Recipient address rejected: example.com greylisted for 60 seconds by ZEROSPAM
The receiver could not confirm the recipient address on this attempt. If the retry keeps failing, treat the address as invalid and remove it.
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 ZeroSpam, 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 ZeroSpam's postmaster documentation.