Get-Mailbox -Identity $userprincipalname |
    
    # Loop through all the emailaddresses
    foreach { 
       $a = $_.emailaddresses
       $b = $_.emailaddresses
     
     # Remove all but $keepmail
       foreach($e in $a) 
           { 
           if ($e.tostring() -notmatch $keepmail ) 
               { $b -= $e; } 
           $_ | Set-mailbox -EmailAddressPolicyEnabled $false -emailaddresses $b -alias $userprincipalname
           }
    }
    
    # We had to remove the emailaddresspolicy to make changes. Let's reactivate it
    Set-mailbox -Identity $userprincipalname -EmailAddressPolicyEnabled $true
}