+* lynx (for converting HTML messages to text)
+* Perl and several modules: (Debian package name)
+ - CGI perl-modules[1]
+ - Date::Parse libtimedate-perl
+ - Email::Address libemail-address-perl
+ - Email::Filter libemail-filter-perl
+ - Email::MIME libemail-mime-perl
+ - Email::MIME::ContentType libemail-mime-contenttype-perl
+ - Encode::MIME::Header perl
+ - File::Path::Expand libfile-path-expand-perl
+ - IPC::Open2 perl
+ - IPC::Run libipc-run-perl
+ - Mail::Thread (2.5+) libmail-thread-perl
+ - URI::Escape liburi-perl
+ - XML::Atom::SimpleFeed libxml-atom-simplefeed-perl
+
+[1] - Only required for serving/generating Atom and HTML pages.
+ Keep in mind this will be split into a separate Debian package
+ when CGI.pm is dropped from the Perl standard library.
+ Plack/PSGI, FastCGI, and mod_perl2 will all be supported.