problem:

How to add additional Emails to a Azure AD Connected to Office 365




First, log onto your local AD, then go to Active Directory Users & Computers MMC. From there, click the View along the top and enable Advanced Features.




Now, close the MMC and go back in, find your user and go into the properties, you should now see a new tab called Attribute Editor. In there you will find an attribute called proxyAddresses.




You need to add all the addresses you want in here; prefixed with smtp: (lowercase)




Your primary address should start with SMTP: (yes uppercase!), all the others should be lowercase.




It should appear blank at first, you will need to add the current email address as




SMTP:username@domain.com
and the new alias as smtp:useralias@domain.com.




Either we can wait the default 30 minutes to sync new data to Office 365 or go to your AD Connect server and perform a manual sync.