To summarize the many kind messages received by:
procmail(_at_)Informatik(_dot_)RWTH-Aachen(_dot_)DE
comp.mail.{misc,sendmail,headers}
An illegal message-id in a valid (non-intentionally-done-for-spam) message
occurs, but, only when there is "something" wrong with the user's mail
handling system.
A second universal conclusion was that, an illegal message-id will
not, in itself, cause anything bad to happen to any other program (other
than being filtered out by illegal-message-id filters).
Thanks,
John Gianni
Cadence Design Systems, Inc.
San Jose, California, USA