you can use this Linux shell command to process
sendmail -qp5m
       -qp[time]
              Similar to -qtime, except that instead of periodically forking a
              child  to  process the queue, sendmail forks a single persistent
              child for each queue  that  alternates  between  processing  the
              queue and sleeping.  The sleep time is given as the argument; it
              defaults to 1 second.  The process will always sleep at least  5
              seconds if the queue was empty in the previous queue run.