The Confusing Case of Cross-Forest Delegation
If you've even participated in an Exchange Online migration at almost any level, it's likely you've run into the issue of cross-forest delegation. You know that Exchange allows you to delegate rights from one mailbox to another, allowing users to access other mailboxes. When you do an Exchange hybrid migration, there are some special considerations you have to take to keep these delegated rights working. Depending on who you ask, you'll get all kinds of different answers about what works when. In this blog post I will explain the confusing case of cross-forest delegation, and what you can expect to work or not work.
There is no cross-forest delegation
Much of the success of Office 365 is built on the Exchange hybrid migration. Since the initial release of Office 365 it has been possible to connect your on-premises Exchange organization to Exchange Online and have the two organization work almost like a single Exchange deployment. In the early days getting hybrid to work was a long and complicated process, but it was possible. The introduction of the hybrid configuration wizard has made the process of configuring hybrid Exchange much better.