> That would be rather harsh for that user.. (S)he may be unreachable only
> for a few days, although this is NOT the case, usually.
 
I disagree with the first part, I don't care whether the second is
true, and I always assume the third (the user is permanently
unreachable.)  As owner of one small, low volume list, I always
immediately delete any user who causes mail to be bounced to me,
unless the bounce is due to an "unable to connect to host" message
from the Interbit.  (I'm a bit more tolerant of this particular
problem because it's not the user's fault, and it's often not the
target site administrator's fault either.)  I run a mailer that
*NEVER* bounces validly addressed mail to a valid userid.  I will not
cater to those sites that run stupid mailers that bounce mail if the
phase of the moon is wrong.  (Did I mention u**x?  Nah, I wouldn't use
4 letter words on the network.)  If the user that I drop due to
bounced mail doesn't like it, it's his/her responsibility to beat on
the local administration to get a decent mailer.  I'm certainly not in
a position to do that, and I resent suffering from it.  If the users
at those sites suffer, then THEY are the ones in a position to
pressure the right people to fix the mail system.