A messaging system interacts with the messaging applications of customer, admin, and agent clients to support encrypted communications among customers and businesses. To register as an agent of the business, an agent client sends registration information to the messaging system and receives a barcode in response. The messaging system validates information about the barcode received from the admin client and sends a validation code to the admin client. The admin client displays the validation code, and the validation code is entered into the agent client. The admin client generates a membership list including an agent client identifier, digitally signs the membership list, and provides the signed membership list to the messaging system. When a customer messages the business, the messaging system forms a customer group using the signed membership list and distributes the message to the agent clients in the group.