Mulberry is one of the best IMAP clients, developed where IMAP originated with the Cyrus IMAP server by the same Cyrus Daboo. It is now republished as a free application, the source is openly available ().
Would it work standalone from a USB drive, or would somebody care about converting it to a PortableApp or U3P?
I just started to use Voyager, the portable version of TheBat! (), but I'm not yet sure about the relative merits of both programs.