So I was trying to figure this out last night and everyone online was indicating that the only way to do this under sense was to get Touchdown or RoadSync or something like that. This just isn’t true. The AOSP (Android Open Source Project) email client not only supports multiple exchange accounts, but it will automatically sync your contacts AND calendars, too. So how do you get the AOSP mail client installed? Well the good folks over at Cyanogenmod have a copy of it in their ROM. Download the entire ROM and you can extract just the apk that we’re interested in and install it via root explorer, file manager, or something like that. It’s in the \system\app folder. Once you’ve gotten it installed, just open up the email application (different than the sense Mail.apk) and get to work. Create the new exchange account and tell it to sync calendars and contacts (if you want). These accounts will even show in the Sync settings.
Please note that I verified this works with 2.2 Froyo version of the HTC Sense ROM for Evo. If you have any difficulties, feel free to let me know.