In Threema Broadcast, all messages are always transmitted in encrypted form. On top of that, incoming messages are not stored (unless the option “Save chat history” is enabled in centrally managed group chats).
Messages sent via the Threema Broadcast web interface are protected using TLS while in transit between your browser and the Threema Broadcast server. The Threema Broadcast server then encrypts the messages again using Threema’s regular end-to-end encryption based on NaCl. The private key of a Broadcast ID is stored in symmetrically encrypted form for each customer to prevent unauthorized access by third parties.
For more information, please refer to the section “Usage Data” of Threema Broadcast’s Privacy Policy.
