This script is not always reliable and sometime will fail to restart sendmail. This generally happen when sendmail is delivering mails to other systems (There are several sendmail process running).
After this failed restart, sendmail is not accepting email anymore. The solution is to stop the service and start it.
Some people have changed the script with a "killall sendmail" in the restart section to make sure the restart is always successful.
Note that restarting sendmail is not something we do often.