NAME

       lei-mail-formats - description of mail formats supported by lei

DESCRIPTION

       lei-q(1) supports writing to several existing mail formats for interoperability with
       existing mail user agents (MUA); below is an overview of them to help users choose.

Maildir

       The default output format when given a filesystem path, it supports parallel read-write
       access.  Performance is acceptable for smaller directories, but degrades as mailboxes get
       larger.  Speed and scalability are limited by kernel and filesystem performance due to the
       use of small files and large number of syscalls.

       See also: <https://cr.yp.to/proto/maildir.html> and
       <https://wiki2.dovecot.org/MailboxFormat/Maildir>

Mbox family

       The mbox family consists of several incompatible formats.  Locking for parallel access is
       supported, but may not be compatible across tools.  With compression (e.g. gzip(1)), they
       require the least amount of space while offering good read-only performance.

       Keyword updates ("Status:" and/or "X-Status:" headers) generally require rewriting the
       entire mbox.

       See also: <https://www.loc.gov/preservation/digital/formats/fdd/fdd000383.shtml>, mbox(5)

   mboxo
       The traditional BSD format.  It quotes "From " to ">From ", but lines already beginning
       with ">From " do not get quoted, thus automatic reversibility is not guaranteed.  MUAs
       which favor "mboxcl" or "mboxcl2" may convert these automatically to their preferred
       format.

       Truncation is undetectable unless compressed with gzip or similar.

   mboxrd
       An evolution of "mboxo", but quotes "From " lines prefixed with any number of ">"
       characters and is thus fully reversible.

       This format is emitted by PublicInbox::WWW(3pm) with gzip.  Since git 2.10, "git am
       --patch-format=mboxrd" reads this format.  "git log" and "git format-patch --stdout" can
       also generate this format with the "--pretty=mboxrd" switch.

       As with uncompressed "mboxo", uncompressed mboxrd are vulnerable to undetectable
       truncation.

       It gracefully degrades to being treated as "mboxo" by MUAs unaware of the format as
       excessive ">From " quoting is recognizable to humans.

   mboxcl
       "mboxo" with a "Content-Length:" header, "From " lines remain quoted to retain readability
       with "mboxo" and "mboxrd" MUAs.  However, it is easy to corrupt these files when using
       tools which are not aware of "Content-Length:" and write out updates as "mboxo".

       mutt(1) will convert "mboxo" and "mboxrd" to mboxcl upon opening.

       See also: <https://www.jwz.org/doc/content-length.html>

   mboxcl2
       Like "mboxcl", but without "From " any quoting.  It is wholly incompatible with MUAs which
       only handle "mboxo" and/or "mboxrd".  This is format is generated by mutt(1) when writing
       to a new mbox.

MH

       Not yet supported, locking semantics (or lack thereof) appear to make it unsuitable for
       parallel access.  It is widely-supported by a variety of MUAs and mailing list managers,
       however.

MMDF

       Not yet supported, and it's unclear if current usage/support makes it worth supporting.

IMAP

       Depending on the IMAP server software and configuration, IMAP servers may use any (or
       combination) of the aforementioned formats or a non-standard database backend.  Currently,
       lei uses Mail::IMAPClient which has acceptable performance over low-latency links.
       Performance over high-latency links is currently poor.

eml

       A single raw message file.  "eml" is not an output format for lei, but accepted by as an
       "--input-format" ("-F") for read-only commands such as lei-tag(1) and lei-import(1).

       Since "eml" is the suffix for the "message/rfc822" MIME type (according to the
       "mime.types" file), lei will infer the type based on the ".eml" suffix if "--input-format"
       is unspecified

       ".patch"-suffixed files generated by git-format-patch(1) (without "--stdout") are "eml"
       files with the addition of an mbox "From " header.  lei(1) removes "From " lines to treat
       them as "eml" when reading these for compatibility with "git-am(1)" and similar tools.

COPYRIGHT

       Copyright 2021 all contributors <mailto:meta@public-inbox.org>

       License: AGPL-3.0+ <http://www.gnu.org/licenses/agpl-3.0.txt>

SEE ALSO

       lei(1), lei-q(1), lei-convert(1), lei-overview(7)