Hi Renniks,
Yes, the HTC Mail app can manage other email accounts (in fact, it can handle Gmail as well, in case you want to have all your emails in a single app, with color coding to tell accounts apart). I use HTC Mail for my work email (Exchange ActiveSync), and use the separate Gmail app for ... well, my Gmail ;-)
The Mail app has a settings wizard for the most common providers like Yahoo Mail and Hotmail, but you can add custom POP3 or IMAP accounts too.
Matter of taste, I guess, but I like the "serious" feel of the Mail app for my work email. It supports threaded view too (sort of groups by conversation).
benitorios