It's been observed that Mailman doesn't play very nice with Virtualmin inasmuch as the web interface is located under the Virtualmin/Webmin address in the form of:
https://domain.com:10000/virtualmin-mailman/unauthenticated/listinfo.cgi
...which is ugly but not insurmountable. Its real failing is that it displays a scary SSL error to people perusing the lists or signing up when the site doesn't have a valid SSL certificate. Granted, you might want to have a valid certificate to be processing user emails and passwords, but let's ignore that for a moment.
Could one get around this problem by making Webmin accessible via both http and https and using mod_rewrite to redirect every part of the interface to https EXCEPT the virtualmin-mailman directory?
I see it's possible to disable SSL in miniserv.conf, and it's also possible to make Webmin listen on multiple interfaces/ports, but is there any way to have an http and https port active simultaneously?