[Mailman-Users] Help interpreting message bounces

[Steve Waage]

M-Users,
    I'm running Mailman 2.1.5 on FreeBSD 5.5 and have been getting lots 
of entries like the following
in my syslog email every morning.
------------------------------------------snip---------------------------------
l8K9iuKg061544     1320 Thu Sep 20 04:44 
<cliccolldev-bounces@[myserver.edu]>
                 (Deferred: Name server: mail2.americantower.com.: host 
name l)
                     <cassadalcassada at americantower.com>
l8L6LsnB067909     1490 Fri Sep 21 01:21 
<cliccolldev-bounces@[myserver.edu]>
                 (Deferred: Name server: tmtb.co.uk.: host name lookup 
failure)
                     <owusutfc at tmtb.co.uk>
l8K8TNKC061094     1551 Thu Sep 20 03:29 <clicref-bounces@[myserver.edu]>
                 (Deferred: Operation timed out with 
ainyx.nnecnisiamsapie.com)
                     <peony-kirkup at ainyx.nnecnisiamsapie.co
-----------------------------------------snip---------------------------------
    The bounce addresses are disguised but legitimate ... the addresses 
that have been
"Deferred" are not on my lists.   I may be missing a basic 
"spam-proofing" setting ??  Or
have they just harvested my listnames in an attempt to get their 
junk-mail past others
email spam-blockers??
    Can I prevent this? 
Thanks,
Steve