On Wed, 27 Feb 2002, Dave wrote:
>
> This is a nearly impossible problem to solve because it is intermittent.
> One reason we switched to LISTSERV for bulk mail was for more reliable
> delivery, and now the client is questioning me on that...

In my experience, such problems are almost always on the receiving end.
Can you telnet to your local email system's port 25 from your Listserv?
Did you check the logs on the recipient system, or only on your Listserv?