I got a new request from my manager to find out how many mails are responded by each person keeping shared mailbox in from field using Send-As permission. I put all the users alias into the csv file and used below command to achieve the goal.

Import-Csv E:\mbx.csv | foreach {Search-Mailbox -identity ($_.users) -SearchQuery “Sent:> $(‘2013-03-31’) and Sent:< $(‘2013-04-03’) and from:’Accounts@mydomain.com'” -TargetMailbox “administrator” -TargetFolder “search” -LogOnly -LogLevel full} | ft Identity, Resultitemscount

Here accounts@mydomain.com is the shared mailbox.

Note: Users should not move/delete their mails from sent items.