To setup an Office 365 email account on an iOS device, perform the following:
1. From the home screen, tap Settings.
2. For best results, it is recommended that this procedure be performed with Wi-Fi turned off (can be turned back on as soon as this is finished). It is not required; however, so if you do not have strong cellular reception at the time you are performing this procedure, you may skip this step.
3. Scroll down and tap Accounts & Passwords (Passwords & Accounts in iOS 12).
4. Tap Add Account.
5 Select Exchange.
6. Fill in the Email and Description fields, then tap Next. Note that the description labels the account on the device and is not visible to anyone else.
7. In iOS 11, account verification is now done via a browser based sign-in process just as you would within your computer's web browser. To proceed, tap Sign In.
8. Enter your Office 365 email address and password on the "iOS Accounts" login page that appears, then tap Sign In.
9. If you entered your Office 365 account credentials correctly, blue check marks will appear next to the Email and Description fields within Settings.
a. Choose the Office 365 services to synchronize, then tap Save. If prompted, tap Keep on My iPhone. Note that other types of iOS devices will display similar confirmation notices.
b. If data is stored in the device's local address book and calendar, those options will be turned off by default. Local data can be enabled, but a pop-up will appear prompting if the user wants to delete the local data because it may result in duplicate contacts or events. Unless the user is sure they don't need this information, the Keep on My iPhone option should be chosen.
10. The account is now added!
If you ever need to update any of your exchange account settings for this device, please refer to the following article: