gnus: Article Identification
6.4.13.7 Article identification
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Articles are stored in the ‘cur/’ subdirectory of each maildir. Each
article file is named like ‘uniq:info’, where ‘uniq’ 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.