Add the option -T after "ezmlm-reject" in the file ..../listname/editor - this will fix the problem.
While it may solve your problem, I wouldn't do it. Requiring the list name to be in the to or cc headers is pretty important in securing the list IMO.
This is without fail true for public lists. If you use private lists that you cannot subscribe oder write to without permission of the list owner, there should be no security problem - such is mine.
