First of all, don't forget to ask your sysadmin to setup autodiscover, as it will make the process of setting up Thunderbird much easier.

Outlook:

Go to Tools -> Account Settings and clic on New

Click on Next

Enter the user's full name, his e-mail address and password. Click on Next

Outlook will search for the web service...

Allow autodiscover.emailarray.com/AutoDiscover/AutoDiscover.xml to configure the client.

The account is now configured. Click on Finish