Your network contains an Active Directory domain named contoso.com. The domain contains Windows 10 Enterprise client com

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Your network contains an Active Directory domain named contoso.com. The domain contains Windows 10 Enterprise client computers.
Your company has a subscription to Microsoft Office 365. Each user has a mailbox that is stored in Office 365 and a user account in the contoso.com domain.
Each mailbox has two email addresses.
You need to add a third email address for each user.
What should you do?

A. From Active Directory Users and Computers, modify the E-mail attribute for each user.
B. From Microsoft Azure Active Directory Module for Windows PowerShell, run the Set-Mailbox cmdlet.
C. From Active Directory Domains and Trust, add a UPN suffix for each user.
D. From the Office 365 portal, modify the Users settings of each user.