Include a Message Recall function
MS Exchange server offers to pull-back sent emails IF not opened by recipient(s). it is good to see it in MDaemon's feature list.
A basic system for recalling messages was added to MDaemon 13.6.1, which can be downloaded from http://www.altn.com/Downloads/MDaemon-Mail-Server-Free-Trial/.
Gonçalo Caeiro commented
With a Flag to keep the disable the Recall Function altogether.
Personally I find that feature a lack of security. If you send an email, sorry, it's out there. One of the things I love in MDaemon is the impossibility of someone recall a message. Specially when I'm receiving Proposals from suppliers. Recalling a message can be legal problem, just imagine that there was a CC and the other guy has a email server that doesn't honor recall. Now you have two persons with asymmetrical information. In negotiations this can be a deal breaker.