Step 1: Launch Mail.
Step 2: From the Mail menu, select Preferences.
Step 3: Click Create an Account (‘+’ symbol).
Step 4: Select Exchange.
Step 5: Fill the following details, and then click Continue,
Name: Enter the email address user's name.
Email address: Enter your email address.
Password: Enter the email address's password.
Step 6: If you receive a warning that "Internet Accounts couldn't log in to the Exchange server...", complete the following and click Continue.
Description: Enter a description for the account.
User Name: Enter your full email address.
Password: Enter the email address's password.
Server Address: Type outlook.office365.com.
Step 7: Click Continue.
Step 8: Select the applications you want to link to your Office 365 email address, and then click Done.
