Adding Allen ISD email to Mail App on iPhone

Go to Settings > Mail > Mail Account > Add Account.
Select Microsoft Exchange
Enter your Allen ISD email address and Description and click Next in the top right corner.
Click Sign In and then Continue on the pop up window
You will be redirected to Allen ISD Portal login page. Enter your username and password and sign in.
On the next screen, Click Save and Allen ISD email will be added to the Mail app on your phone.