<p>This example from <ahref="https://wiki.debian.org/FAQsFromDebianUser#What_is_top-posting_.28and_why_shouldn.27t_I_do_it.29.3F">Debian wiki</a> answers to both, this and next question.</p>
<p>At least <ahref="http://www.debian.org/MailingLists/#codeofconduct">Debian mailing lists</a> and <ahref="http://www.ubuntu.com/support/community/mailinglists">Ubuntu mailing lists</a> forbid top-posting in their guidelines. In my opinion other mailing lists should do this too.</p>