The :any:`notmuch-config(1)` command can be used to get or set
settings in the notmuch configuration file.
-CUSTOM COMMANDS
----------------
+EXTERNAL COMMANDS
+-----------------
If the given command is not known to notmuch, notmuch tries to execute
the external **notmuch-<subcommand>** in :envvar:`PATH` instead. This
allows users to have their own notmuch related tools to be run via the
notmuch command. By design, this does not allow notmuch's own commands
-to be overridden using external commands.
+to be overridden using external commands. The environment variable
+:envvar:`NOTMUCH_CONFIG` will be set according to :option:`--config`,
+if the latter is present.
OPTION SYNTAX
-------------
notmuch --config:alt-config config get user.name
notmuch --config alt-config config get user.name
+.. _duplicate-files:
+
+DUPLICATE MESSAGE FILES
+=======================
+
+Notmuch considers the :mailheader:`Message-ID` to be the primary
+identifier of message. Per :rfc:`5322` the :mailheader:`Message-ID` is
+supposed to be globally unique, but this fails in two distinct
+ways. When you receive copies of a message via a mechanism like
+:mailheader:`Cc` or via a mailing list, the copies are typically
+interchangeable. In the case of some broken mail sending software, the
+same :mailheader:`Message-ID` is used for completely unrelated
+messages. The options :option:`search --duplicate` and :option:`show
+--duplicate` options provide the user with control over which message
+file is displayed. Front ends will need to provide their own
+interface, see e.g. the Emacs front-end :any:`emacs-show-duplicates`.
+
ENVIRONMENT
===========