In one client company I work for, their corporate firewall prevents anyone
inside it from having direct outside email access to the Internet, which
means Entourage, Outlook, etc. can't send/receive to any email account that
is not served by their corporate Exchange server.
However, normal Internet access is provided, and Webmail accounts can be
accessed from inside the firewall through your browser, BUT if you're doing
an email-intensive team project from inside the firewall with lots of
attachments coming and going, webmail's typically stingy server space means
your webmail can be reaching its limit five or six times a day, meaning you
would have to repeatedly log in, type your username/password, tediously
receive and review and then, somehow, manually, move your webmail emails and
attachments to your HD and delete them from the webmail server to restore
capacity. It's a messy hassle.
The best solution I know of, if you can afford it, is to get a cellular
modem that lets you bring your own outside Internet access with you wherever
you go. It's a little card that you plug into your laptop and it has a
little cellphone-style antenna. So you can continue to access the Internet
and send and receive ALL your email with the same email client accounts you
always use...and it all remains in one easily managed location. And you
remain in control of your life.