Our office is new to Office365, and we have had some employees leave recently. We converted the mailboxes to Shared Mailboxes, removed the licenses, and removed the users from our User OU in the domain (into an unsynced, de-privileged OU). We then changed the email addresses of the Shared Mailboxes so that we could "forward" mail directly to a specific person for each account (using "ProxyAddresses", done before, but with a DELETED mailbox).
The ADFS Sync fails because the Shared Mailboxes still have the old email addresses in their ProxyAddresses fields, but I cannot find a way to remove them. There are no options to remove entries in "ProxyAddresses" in the web portal. I removed all reference to the email addresses in our AD from the moved user accounts, still errors. Set-MSOLUser doesn't have a -ProxyAddresses parameter, or a -Remove parameter, like Set-ADUser does. Applying changes to the object returned from Get-MSOLUser does nothing.
So the question is: How do you remove ProxyAddresses from a "Microsoft.Online.Administration.User" object in Office365?