On the sending side Mime::Lite deals with Sendmail or Net::SMTP on unix and will pick what works automagically. Because Net::SMTP will work on Win32 code should port to Win32 seamlessly. On the receive side Mail::Box is an attempt to provide a common access API to different mail box formats.

M$ change their APIs so often you will never have smooth sailing when you try to deal with their stuff. See Microsoft versus GM for an amusing viewpoint on this. Especially the second last point :-)