Your company network includes an On-Premises Windows Active Directory (AD) that has a DNS domain
named contoso.local and an email domain named contoso.com. You plan to migrate from On-Premises
Exchange to Office 365.
You configure DirSync and set all Azure Active Directory (Azure AD) usernames as %username%
@contoso.com
You need to ensure that each user is able to log on by using the email domain as the username.
Which two actions should you perform? Each correct answer presents part of the solution.

A.
Verify the email domain in Azure AD domains.

B.
Run the Set-MsolUserPrincipalName -UserPrincipalName %username%@contoso.onmicrosoft.com –
NewUserPrincipalName %username %@contoso.com Power Shell cmdlet.

C.
Edit the ProxyAddress attribute on the On-Premises Windows AD user account.

D.
Verify the Windows AD DNS domain in Azure AD domains.

E.
Update the On-Premises Windows AD user account UPN to match the email address.

Explanation:
If you have already set up Active Directory synchronization, the user’s UPN may not match the user’s onpremises UPN defined in Active Directory. To fix this, rename the user’s UPN using the SetMsolUserPrincipalName cmdlet in the Microsoft Azure Active Directory Module for Windows PowerShell.
The email domain (Contoso.com) needs to be verified in Office 365.

https://msdn.microsoft.com/en-us/library/azure/jj151786.aspx