I have added a 08 R2 DC with all FSMO roles. I am now adding a EXCH 2010 SP1 server to experiment with. I tried to install and was able to get all roles except the Mailbox role. I get the following error during mailbox role installation - Couldn't resolve the user or group "iforce.local/Microsoft Exchange Security Groups/Discovery Management." If the user or group is a foreign forest principal, you must have either a two-way trust or an outgoing trust. The server is a member server and can ping the 08 DC properly and query DNS. DCDiag passes. I googled the error and recieved advise to run - Here is how to re-create the Discovery Search Mailbox: 1. re-create the mailbox using: Enable-Mailbox "DiscoverySearchMailbox {D919BA05-46A6-415f-80AD-7E09334BB852}" -Arbitration 2. Add permissions to the Discovery Search Mailbox: Add-MailboxPermission -Identity:”mydomain.local/Users/DiscoverySearchMailbox {D919BA05-46A6-415f-80AD-7E09334BB852}” -User:”Discovery Management” -AccessRights:”FullAccess” When I do that I get this error - This task does not support recipients of this type. The specified recipient domain.local/Users/DiscoverySearchMailbox is of type UserMailbox. What am I doing wrong?

Did you post the exact PowerShell command and error message? Run Get-Mailbox "DiscoverySearchMailbox {D919BA05-46A6-415f-80AD-7E09334BB852}" and post what you see.Ed Crowley MVP "There are seldom good technological solutions to behavioral problems."

Hello, Please temporary delete trusted relationship between domains then run the installation again. Thanks, Simon