Step 1: Add a new account in the mail app
Go to your settings –> Mail –> Accounts –> Add Accounts
Step 2: Choose Microsoft Exchange
You want to make sure you are choosing Microsoft Exchange and not Outlook.
Step 3: Input your CIIS email and click ‘Next’
Step 4: Choose Sign In
Step 5: Input your password to your CIIS email
Step 6: Approve Sign-in Request through Microsoft Authenticator
Remember the number that is shown in the sign in request.
Go into the Microsoft Authenticator App.
Enter the number and click ‘Yes’.
Done!
Now you should be able to save and access your CIIS email on the iPhone mail app.