HTC Hero : Receiving Emails - Always Seemed To Work Fine

I've set up Hotmail to be the default email account and has always seemed to work fine (although the sync doesn't always work - when read on the phone, then deleted on a computer, this is not reflected on phone, if that makes sense). However, recently have been having problems receiving emails. I've tried entering the password again; even tried deleting the account and re-setting it up. The former doesn't make any difference. The latter seems to work the first time (with every email coming up unread), but subsequently fails to refresh with new emails.