text_combined: noel jones ubdarhmeganvbhcsorg wed feb 13 2008 105335pm 0500 thomas ledbetter wrote never ending quest block spam get performance mx server postfix configuration tried lowering smtpd_hard_error_count value weve great success past lowering smtp_timeout parameter seemed like another interesting tactic try setting smtpd_error_count lower value immediately saw number messages blocked many errors rise expected analyzing blocked seem like spam stopped however hour situation load average mx servers rapidly started climb necessary revert previous values im thinking messages getting rejected 4xx error code simply queuing remotely overwhelming us resent later make sense postfix issue whatever normal reject code error respond additional 421 disconnect current recipient still rejected sending system real mta still additional recipients deliver make new connection try next recipient something like rcpt 554 invalid recipient 421 many errors goodbye disconnect see evidence log looking postfix configuration parameters although saw change reject code things didnt see smtpd_error_reject_code parameter like one go changing error code 5xx type rejects caused many errors possible reason bad idea normal 5xx code still sent changing 421 code unnecessary violates rfc2821 seeing hosts behave badly 421 disconnect dont want mail firewall general spambots tend come back disconnect real mtas come back orderly manner tuning smtpd_hard_error_limit seems sitespecific probably depends many users many legit mtas sending mail multiple invalid users usually happens user signs mail list account cancelled whatever reason maybe site needs little higher noel jones tue 05 aug 2008 181808 0600 smtpd_error_reject_code