Thanks to everybody for the helpful information on this problem,
which is the most common one I deal with (a result of setting the
lists to accept postings only from subscribers, to avoid spam).  The
double sub / nomail option is one I try to avoid because I see down
the road all kinds of problems with unsubscribing, moving, changing
options, etc.

I've thought that frequently this problem pops up when people buy new
computers and configure their new mail application with what _they_
understand to be their return address, usually a simpler version of
the full address, including internal routing.

This seems to me a fourth possibility to Debra's list of three, and I
suspect it may be the most common.

                                        -- Russ
                                __|~_
Russell A. Hunt            __|~_)_ __)_|~_           Aquinas Chair
St. Thomas University      )_ __)_|_)__ __)  PHONE: (506) 452-0424
Fredericton, New Brunswick   |  )____) |       FAX: (506) 450-9615
E3B 5G3   CANADA          ___|____|____|____/    [log in to unmask]
                          \                /
      ~~~~~~~~~~~~ http://www.StThomasU.ca/hunt/ ~~~~~~~~~~~~