There are log files that you can check to see what the problem
is.  Some problems you might be able to fix at your end
(e.g., tweak some parameters in sendmail).  On the other hand,
I have a list with many users from hotmail.com and from aol,
and have not had problems with those addresses.  However, I
have lots of problems with an ISP in Argentina, "radar.com.ar".
In my case, that's a problem I cannot solve: It seems that
"radar.com.ar" oftentimes, throughout the day, takes its server
out of circulation (yeap---believe it or not!), and this generates,
of course, lots of bounces.

Pardon me for stating the obvious, but some email is bound not
to be delivered:  intermediate nodes might be down, a client's
mbox may be full and its mail is returned, and you have specified
only one or two days of attempts to re-deliver, in order to make
sure that the mail queue does not get too long.

I am not sure what this adds to the discussion, but I guess I want
to stress these three points:

(a) I have not had any "permanent", chronic problems with hotmail
or with aol.

(b) I have had chronic problems with another ISP, which illustrate
the sort of problems that might arise and over which you have no
control (and listserv has nothing to do with it).

(c) In any case, your own sendmail configuration and the real world
out there might well determine that some mail, a very tiny proportion
of it, will be lost. The alternative is that "no mail ever be lost"
at the expense of performance (that is to say, performance may degrade).

Best, elena
====================================================================
Elena Fraboschi                   Email: [log in to unmask]
Indiana University Math. Journal  Phone: (812) 855-4933
Bloomington, IN 47405             Fax:   (812) 855-0046