When you add a deal to DealMachine, you can send mail to the owner at 1 or many addresses.
To add an address, open a deal and scroll to the mailing addresses section.
Then click the "Add Address" button.
If you want to remove a mailing address in the future, you also can. Here's an article that tells you just how to do that: How do I remove an owner mailing address?
Hope this helps! If you have more questions, please reach out to our Customer Support Team using the Help & Support option in your account.
They're available every day including weekends from 9am - 9pm EST.