GrOlsen

To resolve this issue, mount the mailbox store where the System Attendant mailbox is located. If you do not want the System Attendant mailbox to be located on the current mailbox store, you can move it to another mailbox store on the same server.If it useless try Exchange Server Fix Toolbox.It fix corrupted mailbox application repairs email accounts separately and supports the parsing of very large databases.

https://social.technet.microsoft.com/Forums/office/en-US/98da9e16-fdab-4cf9-8251-4f466d6c6c13/server-busy-error?forum=itprovistasp

https://charbelnemnom.com/2016/10/how-to-install-dpm-2016-on-windows-server-2016-and-sql-server-2016-dpm-sysctr-ws2016-sql2016/