To enable multiple message originators to share an SMS shortcode, originator identifying codes can be added to outbound SMS messages that prompt recipients to respond with response messages that include the originator identifying codes. The originator identifying codes can be added by a service provider that administers the SMS shortcode. When a response message is received on the SMS shortcode number, the service provider processes the response message content to extract the originator identifying code. The code and, optionally, a recipient ID can be used as a lookup to determine the intended originator that the response message is for. The response message can then be associated by the service provider with the correct originator for subsequent processing.