SquirrelOutlook is a standards-based webmail package written in PHP4 (Squirrelmail). It includes built-in pure PHP support for the IMAP and SMTP protocols, and all pages render in pure HTML 4.0 for maximum compatibility across browsers.
This package appears to be based on Squirrelmail 1.4.8 (from ReleaseNotes). Unfortunately to make Squirrelmail work on my site I need newer features like Dovcot IMAP for authentication. I and my users really like Squirrelmail 1.4.22, so I was pretty excited when I ran across this package. Most user requests seem to be based on previous Outlook experience. This package is Squirrelmail, and configures the same. I wish it worked here.