See the following page for info about 4.x and Cataclysm: http://my.curse.com/articles/speeddymon/848044.aspx
FuBar_MailFu is a FuBar plugin, originally written by Tekkub to track incoming mail and AH payments, and allow you to see who you have mail from when away from the mailbox, with the catch being that it will only show who the mails are from once you have checked your mailbox.
Please note that this addon is inactive. The current 3.1 release is a minor rearrangement of the TOC and update so it is no longer out of date.
I am currently working on a replacement for this addon, called MailboxPlus, which will incorporate this, and Postman and any user requested features that I can get in there, while still being highly configurable, and small. Until that addon is done, like Postman, I will keep this addon working, assuming Blizz doesnt remove some critical function that it uses.