Articles are stored in the cur/ subdirectory of each maildir.
Each article file is named like
contains no colons.
nnmaildir ignores, but preserves, the
:info part. (Other maildir readers typically use this part of
the filename to store marks.) The
uniq part uniquely
identifies the article, and is used in various places in the
.nnmaildir/ subdirectory of the maildir to store information
about the corresponding article. The full pathname of an article is
available in the variable
nnmaildir-article-file-name after you
request the article in the summary buffer.