SquirrelMail can be extended by a number of plugins, for example, spam filters, and spell checker.
For the operation of Squirrelmail on the web server, no special operating system is required, since it only requires PHP as an interpreter. Are only a web browser and appropriate access to the mail service condition of your use as Webmailer by the user. Many inexpensive web hosts provide an operational Squirrel Mail as default webmail available or offer it for automatic installation.
Since Squirrelmail offers to be a very conservative layout, there are development versions, add the another style. These include the GPL Forks Squirrel Cangrejo, Squirrel Squirrel Overlook and Outlook, as well as Nutsmail with paid skins. The latter has also been devoted to the use on mobile devices, for which the browser detection is a simplified layout is switched.