Mailbox Migration fails with error cannot open “System Attendant Mailbox”.
This error occurs if the System Attendant Mailbox is not accessible. In Exchange Server 2010 Microsoft has made few architectural changes and they removed System Attendant Mailbox from the first database when we install Exchange Server. However the directory object still resides in the configuration partition. This decision was made because of DAG. The same changes has been introduced in Exchange Server 2013, however in 2013 the service Microsoft Exchange System Attendant (aka Mad.exe) itself is removed and the configuration object is still residing in configuration partition.
Figure 1.1 : System Attendant Mailbox error.
In figure 1.1 while moving mailbox the error is generated.
Figure 1.2 : Event Id 1006.
In figure 1.2 Event Id 1006 will get generated if the first default mailbox store is dismounted.
Figure 1.3 : Database Dismounted
Although in the beginning of the article I said there is no System Attendant Mailbox pointing to any of the database, however in the above screen “1st” Database is showing as dismounted. Now the “1st” Database is nothing but “Mailbox Database 0744356392” which is the default one. I have renamed it to “1st” for administrative purpose.
Renaming the database wont cause any problem, however keeping the database offline can cause many problems.
All arbitration mailbox resides in the default mailbox database and these mailboxes play very important role.
Figure 1.4 : Arbitration Mailbox
In figure 1.3 it gives us clear picture that the default Mailbox database holds important mailbox and should not be kept dismounted under any circumstances. Lets go ahead and mount the store.
Post Mounting the default store Move Mailbox succeeded without any problem.
Important : Rename the default mailbox store only when need arises. Renaming it will not cause any kind of downtime, however it is also very important to a make a note of what role the database is holding before renaming it. Since special system mailboxes resides in this database and keeping it online is mandatory.
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