On Thu, 18 May 2000 19:42:11 -0400, Don Wiss <[log in to unmask]> wrote:

>Has your ISP implemented some new spam blocking and is now filtering out
>messages that have a null return path?

The quick test for this condition is send one message to LISTSERV@...
with the 2 line command:

command message:   THANKS
                   INFO listname      (name of your list)

You should get 2 separate responses back.  The command acknowledgement and
response to THANKS is sent with RFC821 return-path  MAIL FROM:<>  which is
sometimes blocked (in violation of internet mail standards, see our FAQ at
http://www.lsoft.com/manuals/lsv-faq.stm#5.16)

The 'file under separate cover' (response to the INFO command) is sent with a
(non-blank) return-path of owner-listname@... and will not be blocked for being
blank.  So if you get only one response (the second) you have strong indication
of blocking.  If you get 2 responses consistently, then it is probably not a
blocking problem.