Well, one snag in your outlook is that LISTSERV(tm) doesn't deliver mail - it only generates mail.  You have an SMTP agent somewhere that actually delivers mail.  When you see that "...posted via..." log entry, it only confirms that the SMTP agent accepted a message from the lists server for that recipient.  To pursue the non-receipt problem further, you'll need to research the SMTP agent logs - look for what happened when it contacted the target site mailserver.

>>> [log in to unmask] 02/27/02 03:30PM >>>
> There are a bezillion reasons why folks don't always get
> their email.  A
> comprehensive analysis would require knowing the userid@host
> in question,
> having them send some test messages to LISTSERV, having
> access to logs,
> using NSLOOKUP (perhaps recursively), sometimes contact with
> postmasters
> and ISPs (any blocking going on), etc.

The problem is, even LOCAL users have reported this problem. And
recently I have reproduced it with my own E-mail address which has never
experienced any problems.

When the LISTSERV log reads "Mail posted via SMTP to ..." and there is
no subsequent indication in of a delivery error to that address, it
indicates to me that the SMTP transaction was successful (i.e., no DNS
or transient errors).

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...