Correct, the picture is coming through their MMS system via email. However if you attempt to email back to an MMS address it will most likely go nowhere (unless they've spent the time to set it up). Using the same address to the vtext domain will go through the SMS center (rather than the MMS center) and can be delivered to the customer. It will come over as a short message (although the old 165 character limit is pretty much non-existent these days).