Dueling duplicates

[Ian Zimmerman]

I am confused by what seems like 2 separate duplicate article handling
mechanisms in Gnus.

First, there's "Duplicate Suppression" (manual section 3.30), tweakable
with the following variables:

`gnus-suppress-duplicates'
     If non-`nil', suppress duplicates.

`gnus-save-duplicate-list'
     If non-`nil', save the list of duplicates to a file.  This will
     make startup and shutdown take longer, so the default is `nil'.
     However, this means that only duplicate articles read in a single
     Gnus session are suppressed.

`gnus-duplicate-list-length'
     This variable says how many `Message-ID's to keep in the duplicate
     suppression list.  The default is 10000.

`gnus-duplicate-file'
     The name of the file to store the duplicate suppression list in.
     The default is `~/News/suppression'.

And then there are "Duplicates" (manual section 6.3.11), which deals in
the following:

`nnmail-message-id-cache-file'

`nnmail-message-id-cache-length'

`nnmail-treat-duplicates'

What is the relation between these and which is normally active?  Both?
Neither?  Does it depend on the select method?  I'm interested mainly in
the answer for nnimap as that is my primary method.

-- 
Ian Zimmerman
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