When you require a queue/dequeue method for hosting and releasing your email, we recommend using On-Demand Mail Relay (ODMR) whenever possible. This method is superior to ETRN and other methods in that in requires authentication before mail is released. Further, it utilizes an ESMTP command called ATRN that does not require the client to have a static IP address, because it immediately reverses the flow of data between the client and server, releasing the messages without having to make a new connection to do so (unlike ETRN).
MDaemon fully supports ODMR on the client side via using the ATRN command and authentication controls on the Mail Release screen, and on the server side using the Domain Gateways features on the Dequeuing screen of the Gateway Editor.
Some mail servers do not support ODMR, therefore you should check with your provider before attempting to use it.