There are a couple spots in DealMachine where you can see your sent mail.
On the deal dashboard, this example says "Sent 1 time." you might also see:
- Pending Approval (means you need to open the deal and click "Start Mailers")
- In mail queue (means you already clicked "Start Mailers" and your mail will be printed in the next 5-15 minutes)
On the deal screen, slide up the Activity, Notes, and Messages slider and you can see when the mail was sent. You can also track the mail piece, see expected delivery, and also when the deal was delivered.
Those are two simple ways to see when your mail was sent!