If num is zero, this caching feature is
turned off. A value of 1 is good for workstations that forward all mail to a central mail
server and is the default that is used if this option is entirely missing. When configuring
withth e mc technique, the default is 2. A value of 4 is the maximum for most machines
that forward mail directly over the Internet. Higher values might require that you increase
the number of open files allowed per process at the system level.
Caching is of greatest benefit in processing the queue. V8 sendmail automatically adapts to
conditions to avoid caching connections for each invocation of sendmail. Maintenance of
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988 | Chapter 24: The O (Options) Configuration Command
an open connection can delay return to the user??™s program, for example, and too many
open connections to a common target host can create a high load on that host.
Beginning with V8.13, this option affects delivery agents that receive messages using SMTP
over the standard input/output (that is, with P=[LPC]).
When caching is enabled with this ConnectionCacheSize option, the Connection-
CacheTimeout option should also be declared to set the connection timeout. The
ConnectionCacheSize option is not safe. If specified from the command line, it can cause
sendmail to relinquish its special privileges.
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