OK, so you have installed Firefox and love it: why not switch your email client too? Thunderbird has all the features you want:

Safe and Secure

Government grade security features such as S/MIME, digital signing, message encryption, support for certificates and security devices.

Spam filtering

Adaptive rules - Thunderbird learns how you define spam!

Multiple email accounts

Maintain individual inboxes for each of your email accounts.

Built-in RSS reader

Extensions and Themes

Change the look and feel of your email interface.

Setup lets you import all your details from Outlook (Express) so there is no excuse for not switching!