Why a message was rate-limited or rejected at SMTP time

Sometimes a sender reports that their mail bounced immediately rather than being quarantined. That means MxGuard refused it during the SMTP conversation — it was never accepted, so it will not appear in your quarantine.

Common causes: - DNSBL block. The sending IP hit three or more of the six connection-time blocklists and was refused at postscreen. - Rate limit. The source exceeded 30 connections/min, 60 messages/min or 100 recipients/message. Legitimate bulk senders should slow down or split their sends. - Recipient rejected. The address doesn't exist on your backend; MxGuard's SMTP-time recipient probe failed, so the message was refused (this is by design — it prevents backscatter). - Score ≥ 0.97. The message scored high enough to be rejected outright with a 550 response.

Because rejected mail is never stored, the fix for a false rejection is an allow rule (by sender, domain or IP/CIDR) so the source bypasses the check that caught it.