This came in today:
~/$ apt-cache show icedove
Maintainer: Alexander Sack
Replaces: mozilla-thunderbird, thunderbird, mozilla-thunderbird-offline
Provides: mail-reader, imap-client, news-reader
Conflicts: mozilla-thunderbird (<= 1.5-2), thunderbird (>= 22.214.171.124-2), mozilla-thunderbird-offline ...
Description: free/unbranded thunderbird mail client Icedove is a
unbranded Thunderbird mail client suitable for free distribution.
The goal of Thunderbird is to produce a cross platform stand alone
mail application using the XUL user interface language.
Icedove/Thunderbird leaves a somewhat smaller memory footprint than
the Mozilla/Seamonkey suite.
Let the flame wars begin :p
Update: somebird would have suited better for a rename ;)