Unable to change default email address for Office 365 user

Office 365 user - unable to change their default email address. We are a partial hybrid organization with remnants of Exchange 2007 still in place on-site. The default sent address for a new user that has been setup is the <companyname>@<companyname>.onmicrosoft.com  I am unable to change in Office 365 via console. Of course, there is the "some changes need to be done in active directory...blah blah blah"notice but there is actually no way to make this change within active directory. Any ideas? Is there a way to make this change using Powershell??
Jason ShawAsked:
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Éric MoreauSenior .Net ConsultantCommented:
have you correctly added your domains to your Office 365 tenant?
Jason ShawAuthor Commented:
Eric - Yes. We have been running for a few years now and just noticed this with a newly-added user.
Vasil Michev (MVP)Commented:
You can use the -WindowsEmailAddress parameter as a workaround:

Set-Mailbox mailboxname -WindowsEmailAddress whatever@tenant.onmicrosoft.com

Open in new window

This will set whatever@tenant.onmicrosoft.com as the primary SMTP, while keeping the current one as secondary. It will work against synced users too.
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Michal ZiembaIT AdministratorCommented:
Are you using Azure AD Sync to get your users accounts in sync with Office 365?
If yes, then you need to change the ProxyAddress field on the AD object.
timgreen7077Exchange EngineerCommented:
where does the user mailbox reside? is it on-prem or in o365?
Jason ShawAuthor Commented:
Mailbox is in Office 365...per Michael comment - If  user setup in AD and sync with Office 365 for passwords, I change the proxyaddress field in local ad?
Jason ShawAuthor Commented:
I made change to the user/mailbox using Powershell. Office 365 console does show default email is now correct ( user@ companyname.com) but when user sends an email it shows sender as user@companyname.onmicrosoft.com....am i missing something?
Vasil Michev (MVP)Commented:
Changing the default SMTP address doesnt mean it will be automatically changed in Outlook too. You have to recreate the profile for that: https://support.microsoft.com/en-us/help/3040795/smtp-address-in-user-s-profile-doesn-t-change-when-primary-email-addre

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timgreen7077Exchange EngineerCommented:
if the mailbox is created in office 365 you need to set the reply address in exchange online. in o365 go to admin center > exchange > mailboxes and double click the user mailbox then go to email address and double click the correct email address or add it and select the check box "make this reply address" and save it. this will sent the emails with the correct address. this doesn't change user sign in or anything.
Todd NelsonSystems EngineerCommented:
Sounds like we are all grasping at straws here to provide a resolution, so I'll throw in my two cents as well...

How are your email address policies configured in the on premises Exchange?

Supposing the users in question are synced from on premises, the changes you are attempting to make cannot be made in O365.
If you are in a hybrid setup and the mailbox was since from onprem to 365, all changes need to be made onprem
Seth SimmonsSr. Systems AdministratorCommented:
No comment has been added to this question in more than 21 days, so it is now classified as abandoned.

I have recommended this question be closed as follows:

Accept: Vasil Michev (MVP) (https:#a42453126)

If you feel this question should be closed differently, post an objection and the moderators will review all objections and close it as they feel fit. If no one objects, this question will be closed automatically the way described above.

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