Use Horde or Roundcube for Webmail.
By default, new installations of cPanel & WHM version 76 and later do not include SquirrelMail.
Deprecation: cPanel & WHM version 76
Removal: cPanel & WHM version 78
How SquirrelMail came to cPanel
SquirrelMail was added to cPanel back when webmail first became an option for cPanel users more than a decade ago. It hasn’t changed much in appearance or feature set since its introduction. Few webmail applications have provided such a stable, feature-rich experience. Its stability drew a faithful following among all types of users. Technical support personnel especially appreciated it, because of its predictability. While other webmail applications failed, SquirrelMail was reliable.
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 other things take priority. When that happens, its users often leave as well.
SquirrelMail’s last update was May 30th, 2013, with their last release on July 12, 2011. In that seven years, 4 versions of PHP have reached End of Life, and we have worked with others in the community to maintain SquirrelMail. Unfortunately, recent security patches have significant problems, forcing us into a choice. Exclude the security fix and ship SquirrelMail with known security flaws, ship a secure version with known interface issues, or attempt to fix the problems.
Webmail users now expect a better experience than SquirrelMail provides. Rather than continuing to ship an unmaintained application, we decided to remove SquirrelMail.