From time to time, we (list-owners) receive notification of delays from
a product that runs on many different sites e.g.,

Symantec_AntiVirus_for_SMTP_Gateways@host

and it will say something like:

our message with Subject: blah-blah-blah

could not be delivered to the following recipients:

userid@node


Please do not resend your original message.

Delivery attempts will continue to be made for nn  day(s).

--

It has been my experience that these warnings trigger in as little as
five minutes!  Furthermore because of the name of the apparent server
application that is generating it, it seems that it is being delayed due
to anti-virus/spam processing.

I'd really wish that these "nag" messages were not generated as quickly
as they appear to be ... they seem to consume needless bandwidth and
list-owner attention.

/Pete