[throw0101a]

> The latest stable version 1.4.23-svn is tested with PHP up to version 7.3 and replaces version 1.4.22 which can only run on PHP version 5.0-5.4.

* https://en.wikipedia.org/wiki/SquirrelMail

FreeBSD's Ports has 7.4 and 8.0:

* https://www.freshports.org/mail/squirrelmail/

There's always Roundcube.