When you want to change an email address on a Mailbox in Office 365 you get the following error message:
The operation on mailbox “<mailbox>” failed because it’s out of the current user’s write scope. The action ‘Set-Mailbox’, ‘EmailAddresses’, can’t be performed on the object ‘Stacey Brown’ because the object is being synchronized from your on-premises organization. This action should be performed on the object in your on-premises organization.
This issue is caused by the fact you’re synchronizing user objects from a local Active Directory using DirSync or WAADSync, and you want to change properties in Office 365. This is not possible since the Source of Authority is your local Active Directory, and not Windows Azure Active Directory. This means you have to change all the user’s properties in Active Directory, including his email address.