Some providers use one email address to send email and another for receiving email.
Listserv does not seem to recognize Reply-To in messages, only the FROM field when determining if the sender is authorized to send a command or post. But it is worth trying to set the replyto field in email programs to see if that will make a difference, sometimes it seems to. Go to each email program's link for howto on changing replyto. In Control Panel, double-click Mail And Fax. On the General tab, click Message Format, then click Character Set.