Set up Mail.app for Exchange OWA - iPad mail fine, Mail.app not

I am getting increasingly confused and web searches haven't helped solve my problem.

I have a company Exchange account which I can access via Outlook webmail - the information I have works with Entourage 2004, and using the mail app on both my iPad and iPhone.

However, trying to use Mail for the same purpose (Entourage gets a little long in the tooth) or even Outlook for Mac 2011, fails because the account set up wants information that I don't have (and can't get because the company IT guys have no idea if you mention Apple Macs.

In essence, for both iPad and iPhone, I can enter:

Server: webmail.mycompany.com
Domain: mycompanystuff.com
Username and password

And my email, calendars and contacts list update beautifully.

Entourage needs essentially the same basics.

But Mail demands incoming mail server, outgoing mail server, doesn't mention domain, and won't connect whatever combination I put in, whether to IMAP, Exchange or Exchange IMAP.

I trialled Outlook 2011 and it seems to mirror the questions for Mail.

I'm at a loss as to how to solve this with the information I have. It may not be soluble, but it does seem odd that I can access the account from mobile devices like iPad etc and an older program, but not the newer computer based one.

Any advice? Thanks in advance, even if you can't help!