In Exchange 2010 and 2013, when you configure “send as” and “send on behalf” for a mailbox or shared mailbox, by default the sent emails are only copied to sender’s sent box but not from’s mailbox.

If multiple persons have access to the same mailbox or shared mailbox, they may want to see the email/reply sent by other persons so that they are aware of the status/conversation.

To copy sent emails to both sender and from mailbox: