Are you using the HTC mail app? I find that the best method for using Mail is not the "preset" account setups for Hotmail or Yahoo, etc, but just do a pure IMAP or POP3 setup. on your computer, Hotmail should have some instructions on how to setup your account via IMAP, then on your phone, select IMAP setup instead of WL Hotmail.
Also, there is now a Hotmail app for Android, you could try that if HM is the only mail account you want