is there a way in mailman to disable replies to newsletters ? I mean that any replies detected by mailman is discarded automatically.
Mailman can be configured to only allow messages to the list address from list owners or moderators. Basically you want to set everyone's mod bit, then enable the option that sets the mod bit for all new members. Then make sure to list approved posters as either owners or modeators. After doing this, anyone else that attempts to post to the list address will get an NDR message back from mailman.