Maintaining a cached connection to another host (ConnectionCacheSize) imposes a penalty on both the local host and the other host. Each connection means that the other host is running a forked sendmail process (or other MTA) that is either waiting for an SMTP QUIT command to close the connection or for more mail to arrive. The local host has open sockets that consume system resources.

To limit the impact on other hosts, V8 sendmail offers the ConnectionCacheTimeout option. This option tells sendmail how long to wait for another mail message before closing the connection.

The forms of the ConnectionCacheTimeout option are as follows:

O ConnectionCacheTimeout=wait       configuration file (V8.7 and later) 
-OConnectionCacheTimeout=wait       command line (V8.7 and later) 
define(`confMCI_CACHE_TIMEOUT',wait)    mc configuration (V8.7 and later) 
OKwait                              configuration file (V8.6 and later) 
-oKwait                             command line (V8.6 and later) 

Optional whitespace can precede the wait. The wait is of type time and specifies the period to wait before timing out a cached connection. If this option is entirely missing, the default (for both the configuration file and the mc configuration technique) is 300 seconds (five minutes). When specifying the wait, be sure to include a trailing s character. If you don't, the number that you specify is interpreted by default as a number of minutes. The wait should never be longer than five minutes. A value of 0 essentially turns off caching.

This ConnectionCacheTimeout option has an effect only if the ConnectionCacheSize option (ConnectionCacheSize) is also declared.

The ConnectionCacheTimeout option is not safe. If specified from the command line, it can cause sendmail to relinquish its special privileges.