Removing email proxy addresses from AD (helpful if you sync your AD to Office365)

Right now, this is a partial post while I get the PowerShell scripting components together. I needed to remove all the proxy addresses for a certain domain in advance of removing that certain domain from our Office365 account. Because we sync our local AD with Office365, I need to remove the proxy addresses from the local AD.  I could do this manually, of course - which is long and inefficient.  The crucial command I used is this one:

Set-ADUser username -Remove @{ProxyAddresses="smtp:username@domain.com"}

I ran this from "Active Directory Powershell for Windows PowerShell"

Because I'm not good enough with PowerShell yet, here's what I did.  I tried to remove the domain from the account in Office365.  Office365 returned all the mailboxes that had the domain as aliases.  I copied and pasted the list of mailboxes to Excel.  I extracted the mailbox user names from the list and made a single column in Excel of those mailbox names (in my case - our domain uses a username of joe.smith as the username for Joe Smith) so the single column included Joe.Smith.  Then I did a mail merge with that list to create a get that PowerShell command listed above to be individualized with each username.  And then I copied and pasted those commands into PowerShell.  Not ideal.  Ideally, you'd have a foreach command that would run though all AD users, but this is a story about what I did at this moment.  I'll update this post.