1. History

Click menu [Mail] -> [History] or the History button and the history window will open. You can search there the sending history and export them.

2. Duplicate sending

Of course you do not want to send emails to a certain client repeatedly - that will lead to a very bad impression. To avoid so you can just select "Not Send" option in the "Add Mail" window. Of course you can select "Send".

Select [Tell me if duplicate sending] option will notice you when you are trying to add a duplicate address to the email list.