As you say, it's generally impossible to know what is causing the mail
 delivery failures from the contents of the "countdown" messages.  Nice
 way to describe them by the way. :)  I would recommend sending a note
 the postmaster asking him/her for information.  I've found that sometimes
 such notes actually are the first indication the postmaster has that
 there is a problem.  In those cases, they serve a more important purpose
 than just providing you with an explanation of the mail delivery problems.
 I generally don't mail postmasters at the regional Bitnet/Internet gateways
 since they are providing a generic service, and probably don't know anything
 about most of the machines they are asked to contact via SMTP connections.
 That is, if aardvard.xyz.edu is a workstation that has been down for a
 week, the postmaster at the xyz.edu mail gateway is probably going to know
 what's going on (or can find out).  But the postmaster at your regional
 INTERBIT isn't likely to know more than you've learned from the mail
 rejection notice already.
 
 -jj
 
 PS - I also consider the postmaster to be another person that's been
 bitten by whatever software/hardware problem has caused the delivery
 failure.  So, my notes tend not to be "flames" but rather requests for
 assistance and/or information.  There are exceptions of course, but
 you'll have to decide for yourself if/when the bounces are caused by
 unforseeable hardware/software problems or negligence and phrase your
 responses accordingly.