Sendmail has a number of starting options. We will only give a brief over view of the common commands. You should read the man page for further information.
-bd Run as a daemon. Sendmail will fork and run in background listening on socket 25 for incoming SMTP connections.
-q[time] Processe saved messages in the
queue at given intervals. If time is omitted, process the queue
once. Time is given as a tagged number, with `s' being seconds,
`m' being minutes, `h' being hours, `d' being days,
and `w' being
weeks. For example, `-q1h30m' or `-q90m' would both set the timeout to one hour thirty minutes. If time is specified, sendmail will run in background. This option can be used safely with -bd
So, if you set the time with the -q switch, do not be surprised if your email is not delivered for a while. With Redhat, check the file: /etc/sysconfig/sendmail. It will set the background/queue time so you only need to type:
/etc/rc.d/init.d/sendmail start [Enter] (or restart if it is already running)
Make certain you do not try to start sendmail if it is already running
as you will not accomplish what you want.