When someone first buys XF they receive an email with their licence details. That email is the first point of contact the buyer has (as a customer) with XF. Hence, I'd suggest that it is important to the customer and is a good place to start creating a positive relationship between the customer and XF. The email begins with "Your XenForo purchase (ID xxxxxxxxxxxx) has now been processed and your new items are available in your customer area." My suggestion is to add an opening paragraph to that email, something along the lines of; "Thank you for purchasing xenForo, we are delighted to have you as a customer and will do our best to help support your xenForo website. Please visit our community should you have any questions or would like any advice on using your new xenForo software."