A header containing an URL is added to all messages. Any user can
click on this URL to report a message as spam/not spam. Administrators
later use a different web interface to approve/reject these reports.
Gmane has more stats than you can shake
a stick at.
Mail addresses can be encoded on a
list-by-list basis, and each individual user can override/set
encryption on a message-by-message basis by using the X-Archive
The incoming mail queue is usually pretty short, ensuring that
the archive is very current.
Gmane provides a TMDA-fueled mail
forwarding service usable by anybody.