Cron emails not being sent

Recently, I came across a problem whereby my cron jobs were not sending me email output like they had been recently.  I know I had made some changes installing stuff trying to get greylisting working on my server - which installed some other stuff in addition to the mail server that I already had installed and running.

What I found was, that an easy way to test if you are missing stuff is to use the console "mail" command to test sending/receiving email.  I did this as root user.  I then found that sendmail wasn't installed, and so the email couldn't be sent.

As soon as I installed sendmail, the cron emails started to get sent again.  I made sure I disabled the sendmail service, because I have an email server up and running, and don't want sendmail to start and conflict on port 25.