F=R
Use a reserved TCP port V8.6 and later
The F=R delivery
agent flag causes sendmail to
connect on a reserved (privileged) TCP port for
additional security. Privileged Internet ports are
those in the range of 0 to 1023. Only
root is allowed to bind to
such ports. The sendmail
program calls rresvport(3) to
obtain a socket on its selected port. Note that this
is done only when instantiating an outgoing
connection.
This delivery agent flag is suitable only for use with
the A=TCP
delivery agents. Note that
sendmail is usually started
by root when run as a
daemon.
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