Cannot Migrate Mailboxes via third-party tools in synchronized environment

I happened to run into the same issue twice in one week–once with a large customer, and once with one of our partners. Here's a synopsis of the issue: Mailboxes cannot be migrated via 3rd-party tools because msExchMailboxGuid attribute in cloud is populated due to DirSync/AADSync. In my customer's scenario, they were using ILM 2007…

3