I have a federated hybrid environment with an Exchange 2007 server on premise with Mailbox databases. I had an Exchange 2010 server that bridges the cloud and on premise mailboxes but does not have Mailbox databases.
I have created some resource mailboxes and mail enabled public folders in the cloud. I want on premise users to be able to email these mailboxes. However, the resources don't show up in the GAL and attempts to send emails fails with NDRs that state the email addresses cannot be resolved by the Exchange 2007 server.
My mailbox is in the cloud and I can see all these resources in the GAL and I am able to email them successfully. I can also email the resource mailboxes from external email systems. So the only missing functionality is for an on premise mailbox to email a cloud based resource (or mail public folder).
All other functionality appears ok. We have free/busy and full communication otherwise. We will have merged everything by summer so it's only a problem during the migration.