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
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
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.