vvrpgsporcupineorg andras galos yes reject everybody 4xx fake mx sender see error message one primary mx case error report delay report could something like 421 mx unavalaible similar message appear senders mailboxes cases im afraid answer client receives something could misunderstood client hangup answer need answer fake mx answer unnecessary point failure really say 4xx ill primary mx hangs rcpt many smtp implementations connect backup mx host example qmail postfix versions 21 switch alternate mta already established smtp session instead queue mail try later change postfix implemented primarily keeping intricate smtp engine unchanged delaying handling nonpermanent errors resulted somewhat unusual architecture seems safe way filter mail fake mx connection established rcpt fake mx fake connections say goodbye many spam knock wrong door people taken idea fake mx different level see example openbsd spamd sits front mta passes connections wellbehaved clients real mta misbehaving clients tortured httpwwwualbertacabecknycbug06spamd httpwwwopenbsdorgspamd wietse tue 05 aug 2008 224359 0500 postfix fake mx