The cPanel developers have removed SquirrelMail from the latest version of cPanel. They explain their decision here: https://blog.cpanel.com/the-death-of-squirrelmail/
Why SquirrelMail is being removed
An all too common story with open source projects is a loss of invested developers. A once active, vibrant developer community diminishes as ...
Explanation from Gigenet:
Yesterday, 2/14/19, GigeNET experienced a power outage that temporarily interrupted our services. Here in Chicago, we have experienced many harsh storms this winter which have led to service outages that our systems were able to mitigate. However, these outages must have taken a toll on the electronics of our control ...