If Exchange server on the back-end you can usually use either
OWA (i.e. outlook web access via browser) or Outlook (client software ). OWA doesn't work very well with Firefox (go figure). I use
IEtab to automatically switch to the IE rendering engine within the Firefox.
If you are off-site and using the Outlook client (rather than OWA), it should also be set up to connect to Exchange Server using
RPC over HTTPS (aka Outlook Anywhere) unless your IT people have turned on SSL/TLS support for IMAP connections. You can also set up Thunderbird to connect to Exchange server using HTTPS (see
MozDev Webmail but the OWA file is only available on
Google Groups).