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Postfix Documentation
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General mail receiving performance tips

  • Read and understand the maildrop queue, incoming queue, and active queue discussions in the QSHAPE_README document.

  • Run a local name server to reduce slow-down due to DNS lookups. If you run multiple Postfix systems, point each local name server to a shared forwarding server to reduce the number of lookups across the upstream network link.

  • Eliminate unnecessary LDAP lookups, by specifying a domain filter. This eliminates lookups for addresses in remote domains, and eliminates lookups of partial addresses. See ldap_table(5) for details.

When Postfix responds slowly to SMTP clients:

  • Look for obvious signs of trouble as described in the DEBUG_README document, and eliminate those problems first.

  • Turn off your header_checks and body_checks patterns and see if the problem goes away.

  • Turn off chroot operation as described in the DEBUG_README document and see if the problem goes away.

  • If Postfix logs the SMTP client as "unknown" then you have a name service problem: the name server is bad, or the resolv.conf file contains bad information, or some packet filter is blocking the DNS requests or replies.

  • If the number of smtpd(8) processes has reached the process limit as specified in, new SMTP clients must wait until a process becomes available. Increase the number of processes if memory permits. See the instructions given under "Tuning the number of Postfix processes".

Postfix Documentation
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