NO, once the postcard is completed, it is automatically and immediately processed by a third-party. We have no way of stopping it from being mailed once it is paid for.
https://www.inmateaid.com/ask-the-inmate/can-you-stop-a-postcard-from-being-sent-once-it-is-entered-and-paid-for#answer
Accepted Answer Date Created: April 08,2016