After the first fifty or so bounce notices (since usually the number will
be either one or two or fifty within the first hour of the problem --
one or two meaning it was a temporary glitch, fifty meaning it's a real
problem), I set the subscriber to 'nomail' and send a canned note to
the subscriber and the postmaster.  The copy to the subscriber usually
bounces also, but sometimes the one to the postmaster gets through and
the postmaster lets me know that that subscriber no longer has an account
there.  I've told people on WORDS-L that if they notice an absence of
mail for several hours (which is most unusual on that particular list)
to send the 'query' command to check their mail status.
   --Natalie ([log in to unmask])