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#### 9.19.2 Fetching by `Message-ID` Using the Registry

The registry knows how to map each `Message-ID` to the group it's in. This can be leveraged to enhance the “article refer method”, the thing that tells Gnus how to look up an article given its Message-ID (see Finding the Parent).

The `nnregistry` refer method does exactly that. It has the advantage that an article may be found regardless of the group it's in—provided its `Message-ID` is known to the registry. It can be enabled by augmenting the start-up file with something along these lines:

         ;; Keep enough entries to have a good hit rate when referring to an
         ;; article using the registry.  Use long group names so that Gnus
         ;; knows where the article is.
         (setq gnus-registry-max-entries 2500
               gnus-registry-use-long-group-names t)

         (gnus-registry-initialize)

         (setq gnus-refer-article-method
               '(current
                 (nnregistry)
                 (nnweb "gmane" (nnweb-type gmane))))

The example above instructs Gnus to first look up the article in the current group, or, alternatively, using the registry, and finally, if all else fails, using Gmane.