Winmail.dat files on a Lyris-based listserv

I’m a non-technical person currently serving as an adminstrator for a Lyris-based listserv. Several of our members have sent emails with winmail.dat attachments and all of them seem to be doing so from Microsoft Outlook Web Access programs.
The help I’ve encountered suggests changes at the server-level, but because these are end users (many in large university-based systems) I’m hoping to find a solution that the individual users can implement within their settings. I’d be most grateful if anyone can help. Thanks.