nndiary is a
back end very similar to nnml (see Mail Spool). Actually, it could
appear as a mix of nnml and nndraft. If
you know nnml, you're already familiar with the
message storing scheme of nndiary: one file per
message, one directory per group.
Before anything, there is one requirement to be able to run
nndiary properly: you must use the group
timestamp feature of Gnus. This adds a timestamp to each group's
parameters. Group
Timestamp to see how it's done.