Hi
Go through the following link which explains more about the System Attendant mailbox
http://blogs.technet.com/b/evand/archive/2004/12/21/329172.aspx
If you want to move the System Attendant mailbox to another database, you can do it from ADSIEDIT. Follow the below steps
1) open ADSIEDIT.msc
2) connect to the configuration container
3) Expand CN=Configuration,CN=Services,CN=Microsoft Exchange, CN= "OU Name", CN=Administrative Groups,CN= Exchange Administrative Group, CN=Servers, CN="Server name", CN=Microsoft System Attendant.
4) Right click CN=Microsoft System Attendant and select properties
5) select the attribute "Home MDB". you will find the DN of the database which is currently holding the System Attendant mailbox. you can change this to the DN of the database to which you need to move the System Attendant mailbox.
Let me know if this helps
Thanks