Exchange Hybrid Migration Queries

Question

I've started migrating mailboxes from our on prem Exch 2019 hybrid environment up to Exchange Online.

So far so good with the actual migrations, all has gone smoothly as expected.

I've noted a few anomalies post migration I wasn't expecting however.
I was hoping someone might be able to shed some light on these.

Query 1 - Migrated user mailbox and migrated shared mailbox.
Both users and shared mailboxes that users access have been migrated successfully to EO at the same time, and the shared mailbox delegate permissions remain intact in EO.
When the user tries to access the shared mailbox via Outlook (mailbox previously auto-mapped when originally added on prem) the user cannot access the mailbox.
The workaround - add the mailbox as an additional mailbox to the user profile which solves the issue.
Given that the permissions are intact in EO, is this expected behaviour?

Query 2 - Migrated user mailbox accessing on prem shared mailbox.
Full access permissions granted to the shared mailbox for the migrated mailbox user post migration.
The shared mailbox can be accessed via Outlook client via the migrated user mailbox profile, which was auto-mapped before migration.
Shared mailbox is not auto-mapped in the migrated user profile when accessed via OWA, nor is it accessible when added as a "Shared Folder" - access denied message displayed.

Both of these scenarios are unexpected to me, can anyone explain these behaviours please?

TIA

Answer 1

From what I have seen, typically an hour at most. OWA will work much quicker if they want to access that way - opening another mailbox

Answer 2

The first one happens occasionally. I prefer to remove the full mailbox perms and add them back so they auto-map if desired. If not, your solution works.

For the second one, that is expected.
https://learn.microsoft.com/en-us/exchange/permissions#mailbox-permissions-supported-in-hybrid-environments

Answer 3

Thanks Andy.

I do now recall reading that documentation many months ago to be fair.
Shared mailbox access via OWA is not a major issue in my case, just good to know this is expected behaviour.

The first scenario is the one that is the most troublesome.
If I were to remove/re-add the permissions on the shared mailbox for the affected users in EO, how long before the changes took effect client side in Outlook?

Answer 4

Thanks Andy, appreciated