The HTC email client does not work with Hotmail via Exchange, only POP. This has been noted and documented by Microsoft. Supposedly Microsoft is working with HTC to come up with a fix, but in the meantime, the options are not all that great: sync with Hotmail via POP which is horrible, use the browser, or install the default Android email client, which does not support html in this case, and can only sync one Hotmail calendar. The HTC email client works well with other providers, just not with Hotmail.
This is all documented on the Windows Team blog. Copied from their site:
"Android support: We are continuing to test 2.2 clients against Hotmail, but prioritizing the stock 2.2 client over the vendor modified clients. The standard 2.2 client works well against Hotmail ActiveSync. HTC’s modified client on 2.2 has issues and we are working with them on finding a proper fix. Users have reported success in connecting to Hotmail after installing the stock client for 2.2 on their HTC device."
Hotmail now supports push email, calendar, and contacts with Exchange ActiveSync