Over the last couple of weeks, we have begun receiving a *small* number
of bounces like

Received: from PSUVM (NJE origin LST2SMTP@PSUVM) by PSUVM.PSU.EDU (LMail
          V1.2c/1.8c) with BSMTP id 1036; Fri, 9 Oct 1998 17:42:19 -0400
Date: Fri, 09 Oct 98 17:42:15 EDT
From: <[log in to unmask]>
To: <[log in to unmask]>
Subject: Undeliverable Mail

LISTS.PSU.EDU unable to deliver following mail to recipient(s):
    <[log in to unmask]>
LISTS.PSU.EDU unable to connect for 3 days to recipient host.

to [log in to unmask]  Since we distribute lots of mail from various
lists to those addresses (and sometimes our backlog is signficant), and
my best analysis using SMTP QUEU commands (this is VM/CMS), PING (small
and LARGE packets), SMTP dialogues (full RFC821+822) reveal no problem, I
wonder if their various MX servers are throttling or out of steam?  I
don't think it is an IP-address caching problem.

I've been in contact with MSN.COM support personnel but have gotten no
where, fast.