Just about any and every server needs to be able to send email - whether it's end-user-email, like password recovery services for a website to emails to system administrators reporting on the status of system backups and errors. The problem is that it's non trivial (understatement) to set up a mail server properly.
SkFor any website that requires anyone (users or even just a few admins) to transfer secrets to and from it, you want to ensure the data is end-to-end encrypted. Today various browsers (like Firefox) give warnings when you're sending secret data (like passwords) "in the clear", namely unencrypted.
I have previously provided an in-depth explanation about NextCloud with Collabora Office Online and how we've installed it on Ubuntu 16.04. This is an update both of the process, and of the technology.