Each feed item is converted to following MIME-complaint mail message:
From: "Feed's title" <feeder@localhost> Date: Item's updated/published date, now otherwise Subject: Item's subject Content-Type: text/html; charset=utf-8 [X-URL: link presented in the item] (maybe multiple) [X-Enclosure: enclosure link presented in the item] (maybe multiple) [X-Author: author's name] (maybe multiple) [X-Categories: item's comma separated categories] Base64-encoded item's content. That is HTML as a rule.
Each message is placed under HEX(SHA512/2(title+content)) filename.
Unfortunately many feeds do not provide any date information at all.
Often multiple entries contain the same date. So you can not solely
depend on update/publish date.
mtime is properly set for each newly created mail message. Also
it is set to feed’s update/published date for new/ and
cur/ subdirectories.