I've been using mutt with gmail. It drops into vim when it's time to compose a message. I've never heard of vmail. It sounds interesting, but I would personally recommend mutt over vmail. mutt is quite vimish.
You don't have to store your password in plain text just because it gives you the opportunity to do so - I use mutt without a stored password for IMAP. It means that I have to enter my password between one and three times per day, but that's a minor inconvenience to me.
http://wiki.mutt.org/?UserStory/GMailOverIMAP