I am looking at "mdbox" under Dovecot 2.0beta5.
Looking at the documentation for "mdbox" I saw that we had a directory "storage" containing files "m.#" where "#" is an integer and a map file ("dovecot.map.index").
I think I expected the map file to be a plain text file with one record per line, but in fact it appears to contain binary data.
According to the wiki ( http://wiki.dovecot.org/MailboxFormat/dbox ) the records go as:
map_uid: Unique growing 32 bit number for the message.
refcount: 16 bit reference counter for this message. Each time the message is copied the refcount is increased.
file_id: File number containing the message. For example if file_id=5, the message is in file m.5.
offset: Offset to message within the file.
size: Space used by the message in the file, including all metadata.
The map file I have here is 1688 bytes in size (and I think there are 64 messages stored). Prime factors of 1688 are 2^3 x 211, so I think it is something other than just a straight array of fixed-size structures.
Still, I can always look at the source if I really want to know :-)
Regards,
Bill