Hi tcgadmin,
You can define the search parameters with the command:
New-MailboxSearch <Search Name> -SourceMailbox <Source Mailbox> -TargetMailbox <Discovery Mailbox> -LogLevel Basic -IncludeUnsearchableItems.
To actually run this search, you can use the following command:
Start-MailboxSearch -Identity <Search Name>
Then the search result will show up on the portal.
Thanks,
Chris Ni