When trying to migrate the mailboxes in Exchange, throws the below Error
Cannot open mailbox /o=First Organization/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Configuration/cn=Servers/cn=MAILBOX01/cn=Microsoft System Attendant
Ideally it happens if there is no proper Database Home MDB mapped for Microsoft System Attendant mailbox for the server.
In the ADSIEDIT, Locate the following path,
and map the correct available Database and restart IIS Server using IISREST /NOFORCE.
After service restarted, check the service health and try to move the mailboxes. Belive it will work.