RFC 2369 defines a set of List-* headers that are
normally added to every message sent to the list membership.
These greatly aid end-users who are using standards compliant
mail readers. They should normally always be enabled.
<p>However, not all mail readers are standards compliant yet,
and if you have a large number of members who are using
non-compliant mail readers, they may be annoyed at these
headers. You should first try to educate your members as to
why these headers exist, and how to hide them in their mail
clients. As a last resort you can disable these headers, but
this is not recommended (and in fact, your ability to disable
these headers may eventually go away).
