Last week I received confirmation that some mail sent to me never reached my in box ( in fact mails from that sender have not been reaching me for this month).  I  am trying to trace the problem,  and these articles provide some information.

http://askbobrankin.com/missing_emails.html

http://luxsci.com/blog/wheres-the-email-the-case-of-missing-or-disappearing-messages.html