Currently, the integration uses the Billing Address as the Return Address. This is not very useful for firms with multiple offices that have their own login. When using Stamps.com directly users are able to change which return address is used. Adding this feature to the integration would make it more useful for larger firms.
After investigation, unfortunately the integration does not allow us to build this option in Neos. However, we are introducing the ability to hide the return address so that you can use a pre-printed return address or label in its place.