Connection cache configuration

The Postfix smtp(8) client supports two connection caching strategies:

• On-demand connection caching. This is enabled by default, and is controlled with the smtp_connection_cache_on_demand configuration parameter. When this feature is enabled, the Postfix smtp(8) client automatically saves a connection to the connection cache when a destination has a high volume of mail in the active queue.

  Example:

  /etc/postfix/main.cf:
      
  smtp_connection_cache_on_demand = yes
  

• Per-destination connection caching. This is enabled by explicitly listing specific destinations with the smtp_connection_cache_destinations configuration parameter. After completing delivery to a selected destination, the Postfix smtp(8) client always saves the connection to the connection cache.

  Specify a comma or white space separated list of destinations or pseudo-destinations:

  • if mail is sent without a relay host: a domain name (the right-hand side of an email address, without the [] around a numeric IP address),

  • if mail is sent via a relay host: a relay host name (without the [] or non-default TCP port), as specified in main.cf or in the transport map,

  • a /file/name with domain names and/or relay host names as defined above,

  • a " type:table" with domain names and/or relay host names on the left-hand side. The right-hand side result from " type:table" lookups is ignored.

  Examples:

  /etc/postfix/main.cf:
      
  smtp_connection_cache_destinations = $
  relayhost
      
  smtp_connection_cache_destinations = hotmail.com, ...
      
  smtp_connection_cache_destinations = static:all (not recommended)