In most cases, it is also advisable to install a Mail Transfer Agent (MTA) on your server to enable him to send mails itself.
Why is this useful?
- The system sends a warning or critical states in an email to the user root.
- software like Wordpress send emails when a problem has occurred
- If you want to use the "forgot password" function in WordPress or Seafile, this is done via E-Mail
However, you should be very careful with the configuration so that the own server is not abused by spammers.