Messaging servers, methods and storage media for processing instructions associated with one or more data transfers are disclosed. Exemplary implementations may: receive, at a messaging server and from a computing device, a first unauthenticated message including data transfer instructions associated with the one or more data transfers; perform, by the messaging server, a verification process to authenticate the computing device in order to authenticate the data transfer instructions; assign, by the messaging server and based on authenticating the computing device, a conversation authentication identifier to the first unauthenticated message received from the computing device; and automatically assign, by the messaging server, the same conversation authentication identifier to subsequent unauthenticated messages between the computing device and the messaging server that are associated with the one or more data transfers. A system may authenticate and unify received messages to securely process data transfer instructions, for example from existing email clients.