Tom Ekberg added the comment:

Another mailman expert dug deeper to find out what is going on. Here is
what he said:

  I need to correct myself. The bulk detection feature is a local
  modification to the UW Mailman service.

So that is why our mailman drops 'Precedence: bulk' emails while the un-
modified mailman doesn't.

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<http://issues.roundup-tracker.org/issue2550564>
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