1. Make one of the contacts on the organizational record primary. This will be the person that receives the acknowledgement letter
2. Next, head to Marketing and Communications and click on Address Processing options
3. Take a look at the Standard processing option by clicking the button to the left, then Edit. Note the settings for this Address Processing option. Users will create a new address option to look exactly the same, with the two differences noted in steps 5 and 6
4. On the main Address Processing page, click Add to add a new processing option. Recreate the standard processing option with the exceptions in steps 5 and 6
5. On the Organization tab, choose Primary contact under Contact type
6. We are going to uncheck the box next to Mail to each contact found - as seen here: http://screencast.com/t/TohysZs26S6C
7. The rest of the settings throughout the new address processing option can be the same as what is currently in the standard option
8. Name this Address processing option "Acknowledgements" so that you know what it's for, and Save it

Now, we'll apply that new processing option to your Acknowledgements - 
1. From Marketing and Communications, click on Acknowledgements
2. Scroll down to Processing options, and click Edit
3. For Address processing, choose your Acknowledgements option from the drop down menu, and click Save