FAQ? how to set up a cross-platform encrypted mailing list/forum

[Rachel Willmer]

This might be a FAQ. Or it might just be a question with a really obvious 
answer that I can't see for looking.

How can I set up a mailing list or online forum with encrypted traffic?

The clients are varied platforms: Win98, WinNT, OpenBSD, FreeBSD.

I thought about tweaking the listserver to send out encrypted mails. But 
that doesn't help the inbound traffic.

I thought about using some online forum. But the only one I can find which 
looks to make any mention of the word security is Groove. Which is Windows 
only.

I thought about setting up a VPN between the various mailservers. But we'd 
have to secure all the MX hosts to be sure, and some of them aren't 
adminstratively accessible by me. and anyway one of the potential users 
uses a public ISP,

so um, help! is this a FAQ with no answer? or is this a question with an 
answer so obvious I'll blush when I'm told what it is...

All suggestions welcome...
Rachel