To set up your Exchange account in IOS 11/12:
1) First open the Settings app and open 'Accounts and Passwords'.
2) Now select 'Add Account'.
3) Select 'Exchange'.
4) Enter your email address (description is optional) and then tap Next.
5) Select 'Configure Manually'.
6) Enter your password;
then tap Next
Now enter the server address;
and enter your provided username
8) Enable all the Exchange features you wish to use and tap 'Save'
9) Now when you open the Mail application, your emails should begin to sync with the server.