Strengths and Limitations
Squirrelmail is a fully featured email client that will perform most tasks you expect from any email program.
It is very mature software with a familiar interface, and can be expected to work very consistently from one day to the next, across any number of browsers. In situations where you are using an underpowered computer, or extremely slow internet connection such as you will find in Canada's extreme far north, you will find squirrelmail works better than Round Cube
However, it does not support CalDAV/CardDAV, which means it cannot be configured to sync with those advanced hosting services. It also performs as an old-style web page, meaning you need to click links to make stuff happen. This is different than newer-style web applications, such as Round Cube that behave more like programs installed on your computer