AnyMail was the first 'bigger' application I developed using Perl and the CGI::Application module.
I haven't maintained the application for a long time, and don't plan to do so either.
Please feel free to anymail-downloads.html for educational purpouses, but do not expect it to be bug-free.
If you want a very complete open source webmail client, I recommend SquirrelMail (though it is written in PHP, not in Perl ;-).
This is about how AnyMail was developed.