Greetings all
We are merging 2 companies (forest A source, Forest B target) and migrating all the mailboxes from Exchange 2013 in forest A to Exchange 2016 in forest B (Exch A will be decomissioned). A Two way trust has been established. The Prepare-moverequest script is issued correctly and the New Move is initiated using the ECP "migrate to this forest" from the target forest B Exchange 2016. The mailbox is eventually synched. Until this point access to the mailbox using OWA in Exch A is still functional. However when we finalize/complete the migration and it is definitely removed from Exch A, OWA in Exch A says "something went wrong" when trying to access the mailbox reporting it cannot locate it instead of proxying. Usually (at least between same domain migration) you get redirected or proxied to the target Exchange which has the mailbox. However the Outlook client from the source domain A does update itself and connects to the new Exch Server in forest B correctly so the mailbox is available and online. After the mailbox move we use ADMT to migrate the user from A to B with SID history but filtering MSExch attributes retaining the original user in the source AD. This should not however change the behavior of the source OWA after the mbox has been migrated. Additionally, the source Exch server converts the user mbox into a contact which is the correct behavior so I don't know why from the source OWA it does not proxy correctly towards the target Exch B (maybe some incorrect attribute?). Any pointers are appreciated - thanks!
--- Luca Forattini