Error -2147467259 Invalid mailbox '/o=ExchangeOrgt/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=User (Infostore GUID: 'B2A9BD168D5FD241AB6A25B48A54DB8B') is reported by the Mail Source Agent.
Source Exchange org is Exchange 2010 with a DAG present. The mail source agent successfully logs in to the administrative mailbox, and encounters the "invalid" mailbox error when it tries to login to the mailboxes in the collection.
Permissions have been verified, and MFCMAPI is able to open the source mailboxes using the alias and the Legacy Exchange DN.
Firewall rules were implemented to permit traffic to/from the mail source agent host and the virtual server name for the DAG; traffic to/from the IP addresses of the individual DAG members was being denied.
Configure the firewall to permit traffic to/from the agent host and the individual DAG members.