Maybe they changed IP addresses?

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Date: Fri, 20 Aug 99 10:45:26 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):
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LISTS.PSU.EDU unable to connect for 3 days to recipient host.