Hi Exchange experts, we have complex and struggling scenario here.
Target: Drop dismounted database completely in order release disk space and complete migration.
symptom: EAC when attempt migrate healthy user mailbox to another mailbox database, occurred error "Cannot open mailbox /o=xx/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Configuration/cn=Servers/cn=EX2013MBX/cn=Microsoft
System Attendant" , suspected in the database list possessed 1 dismounted database, therefore attempt to DELETE it, also need to vacate disk space as exchange server already left 150GB.
We are using Exchange 2013 and the initial setup is only 1 mail database that include all the client mailbox, so it is heavily corrupted when the EDB file hit to 800GB.
Results of repair corrupted EDB is failed therefore we create a new mailbox database and mounted it on exchange. the corrupted EDB leave it as dismounted.
And then we delete AD User 1 by 1 and then recreate with same login ID, and point to new mailbox database. (since we tried EAC to migrate mailbox, also used "get-mailbox -database "Mailbox Database 0211395451 | new-moverequest -targetdatabase opsexhgdata" in EMS, both error as corrupted mailbox might not able to migrate anymore)
Now we are stuck at domain administrator account, "Cannot perform this operation on built-in accounts." error pop-up during attempt delete administrator account (to delete mailbox and create to new mailbox database) currently we are unable to use EAC to migrate any user, and also cannot drop the 800GB corrupted EDB file due to built-in administrator still possessed mailbox in the corrupted mailbox database.
Any advice from exchange experts?