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Rmail Babyl
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   The "nnbabyl" backend will use a babyl mail box (aka. "rmail mbox")
to store mail. `nnbabyl' will add extra headers to each mail article to
say which group it belongs in.

   Virtual server settings:

`nnbabyl-mbox-file'
     The name of the rmail mbox file.

`nnbabyl-active-file'
     The name of the active file for the rmail box.

`nnbabyl-get-new-mail'
     If non-`nil', `nnbabyl' will read incoming mail.