Add Primary SMTP Address for Office 365 accounts with Powershell and DirSync

If you are running your local Active Directory with DirSync to Office365, you cannot modify the SMTP address from within the Office365 portal.
This change has to be performed in Active Directory on the Users proxyAddresses attribute.

This script can be used to edit a single user or all users at the same time.

Once the script has run, You can synchronize to Office365 with DirSync