Duplicate elimination

[Dan Weinreb <dlw@exceloncorp.com>]

When a receiving MSH is responsible for eliminating duplicates, it
does so by comparing the messageId of an incoming message with a set
of messageId's of messages that it has already received.  When can a
receiving MSH remove a messageId from this set (so that it will not
grow forever)?  I was unable to find any discussion of this in the MS
document (I'm looking at Message Service Specification, Version 1.0,
11 May 2001).  I am pretty sure that persistDuration parameter
controls this (I believe Chris Ferris said so in recent mail, too).
I'd like to suggest that it would be good if the MS spec came right
out and said this explicitly.

Thanks.
-- Dan