1. One or more non-transitory computer-readable media containing instructions stored thereon, that, in response to execution by a computing device, cause the computing device to perform operations including: generating a message, the generated message including: a first version of a media message comprising one or more content elements; at least a portion of first logic configured to execute in response to display of the first version of the media message on a receiving computer system to cause the receiving computer system to test content-rendering capabilities of the receiving computer system; and at least a portion of second logic configured to display one or more content elements of a second version of the media message on the receiving computer system as replacements for one or more elements of the first version of the media message based at least in part on results of testing content-rendering capabilities of the receiving computer system.