We are in the process of migrating some user mailboxes as part of a pilot for full Office 365 migration.
We currently have an Exchange 2010 server, coupled with a complimenting hybrid and DirSync server. Everything on the directory synchronisation side of things has been working well.
When we have come to migrate on-premise mailboxes to Office 365, we have discovered that permissions haven't migrated, specifically any addition mailbox permissons, send as, send on behalf of and calendar permissions. If we subsequently set these permissions manually, it works.
Microsoft are telling us that these have to be set manually, however this is not what we understand is possible. I cannot believe this is accurate - are Microsoft really stating that you have to set this all manually again? What if you had 100,000 mailboxes to migrate - you would have to document and then set these all from scratch?