Please first attempt to setup your Mac Mail email client as an Exchange account using the auto-discovered settings.
1. Click on the Apple Mail icon
2. Select Exchange as the Account Provider
3. Enter Your Name, Primary GT Email Address, and GT password
4. Select the apps you would like to use with this account and click Done
5. If done correctly, your account will authenticate and launch into Apple Mail.
*Email downloads are dependent on the size of the mailbox, network connection, and bandwidth.