sendmail, 4th Edition

ConnectionCacheTimeout

SMTP connection cache timeout V8.1 and later

Maintaining a cached connection to another host (ConnectionCacheSize on page 987) 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 (5 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 ...