If you do not have the need to run sendmail you are likely better to remove it from your startup scripts. On many systems you will want to look in '/etc/rc.d', here you will have several subdirectories, such as 'rc0.d' through 'rc6.d'. You will want to take a look through each of these directories looking for a file names 'S80sendmail' and 'K30sendmail' (note that the leading numbers will likely vary on different systems). If you remove these files, your system will no longer attempt to load them during startup (or attempt to kill them during shutdown).
If you are concerned about removing a service that you might have a dependency for you can take a partial step, by renaming the file in place. My personal favorite is to change the case of the leading letter to lower case, such as 'S80sendmail' to 's80sendmail'. This allows you to test your changes on the next several start ups and shutdowns, to make sure that you do not have any unwanted nasty surprises (if you discover that you need the service to run simply change the names back). Once you are confident that your change is good to go, then you can go back and remove the files that you had originally renamed.