HP-UX Mailing Services Administrator's Guide

Sendmail 8.13.3
New Features in Sendmail 8.13.3
Chapter 3124
SMTP Pipelining
This feature is an extension to the SMTP service whereby a server can
indicate the extent of its ability to accept multiple commands in a single
TCP send operation. Using a single TCP send operation for multiple
commands improves SMTP performance. SMTP pipelining is an
implementation of RFC 1854 (SMTP Service Extension for Command
Pipelining).
Connection Caching
When processing the queue, Sendmail tries to keep the last few open
connections open to avoid startup and shutdown costs. This only applies
to IPC and LPC connections.
When trying to open a connection, the cache is first searched. If an open
connection is found, it is probed to see if it is still active by sending a
RSET command. If this fails, it is not considered as an error; instead, the
connection is closed and reopened.
The following parameters control the connection cache:
•The ConnectionCacheSize (k) option defines the number of
simultaneous open connections that are permitted. If it is set to 0
(zero), connections will be closed as quickly as possible. This value
limits the amount of system resources that Sendmail will use during
queue runs. The default value is one. You must set this value
appropriately for your system size. Do not set ConnectionCacheSize
to a value greater than 4.
•The ConnectionCacheTimeout(K) option specifies the maximum
time that any cached connection will be permitted to remain idle.
When the idle time exceeds this value, the connection is closed. This
number must be small (less than 10 minutes) to prevent you from
grabbing too many resources from other hosts. The default
ConnectionCacheTimeout value is 5 minutes.
Sendmail 8.13.3 Security
By default, Sendmail is a set-user-ID program. You can set it to a
set-group-ID program by creating a new user smmsp and by using the
submit.cf configuration file. If sendmail is called for initial delivery, you
must use the submit.cf file with a fallback of sendmail.cf as
configuration file.