Squid is a free & open-source full featured web proxy cache server released under GPL 3, which can be used in many other ways like a web server caching daemon to speed up websites loading, cache DNS lookups, filter the traffic and many other network protocols, right now, Squid server supports HTTP and FTP protocols, there is a limited support to other protocols like TLS and SSL, it was first released in 1996.
It is always good to have notification of when a server reboots, especially when you are on vacation, away from the office. In my case, I usually use this on a Linux box that has no video output and no other means to connect to it except ssh.
If you want to use a Gmail account as a free SMTP server on your Debian based server, you will find this article useful. This guide is tested with Raspbian GNU/Linux 8. If you face any issue, feel free to use comments-section below.