We have just set up an Exchange Hybrid environment by running the HCW. It appears that everything completed properly, but now the users with mailboxes still on the on premise server who have been receiving their email on mobile devices using ActiveSync are not receiving any mail. Migrated mailboxes are able to use ActiveSync and get their mail. When you add an account to a mobile device from a mailbox still on the old server, you get an error that says Unable to verify account information. OWA works correctly for migrated and non-migrated mailboxes. Has anyone ever had this come up in an Exchange Hybrid Environment?