I've noticed 818 perl modules(packages) listed on this site

Yes, well that's because they seem to list every mail handling module that they found on CPAN. As I understand it, the Email::* namespace is supposed to be a complete set of modules for carrying out all email processing in Perl - all of which will work nicely with each other. Once that set is complete (and I'm afraid I don't know how far off that is) anything in any of the other namespaces will be redundant.

This is a similar approach to the one taken by the Perl DateTime project a few years ago.