For a Virtual Private Server (VPS) or any other web or other server you should have alerts sent by email for various things. So for example if you automate security updates for an Ubuntu web server you want to be notified if there is some issue with the automatic update.
In order to check and be sure email is setup and working on the sever there is simple command line code to use:
mail -s Test
you then get a prompt to enter
To: [enter the email and press return]
Cc: [press return]
then a blank where you can type in any text you want in the body of the message.
Then you send the message with by pressing CTRL-d
If you don’t receive the email then you can troubleshoot what is going wrong.