lei-mail-formats(5)

1LEI-MAIL-FORMATS(5)        public-inbox user manual        LEI-MAIL-FORMATS(5)
2
3
4

NAME

6       lei-mail-formats - description of mail formats supported by lei
7

DESCRIPTION

9       lei-q(1) supports writing to several existing mail formats for
10       interoperability with existing mail user agents (MUA); below is an
11       overview of them to help users choose.
12

Maildir

14       The default output format when given a filesystem path, it supports
15       parallel read-write access.  Performance is acceptable for smaller
16       directories, but degrades as mailboxes get larger.  Speed and
17       scalability are limited by kernel and filesystem performance due to the
18       use of small files and large number of syscalls.
19
20       See also: <https://cr.yp.to/proto/maildir.html> and
21       <https://wiki2.dovecot.org/MailboxFormat/Maildir>
22

Mbox family

24       The mbox family consists of several incompatible formats.  Locking for
25       parallel access is supported, but may not be compatible across tools.
26       With compression (e.g. gzip(1)), they require the least amount of space
27       while offering good read-only performance.
28
29       Keyword updates ("Status:" and/or "X-Status:" headers) generally
30       require rewriting the entire mbox.
31
32       See also:
33       <https://www.loc.gov/preservation/digital/formats/fdd/fdd000383.shtml>,
34       mbox(5)
35
36   mboxo
37       The traditional BSD format.  It quotes "From " to ">From ", but lines
38       already beginning with ">From " do not get quoted, thus automatic
39       reversibility is not guaranteed.  MUAs which favor "mboxcl" or
40       "mboxcl2" may convert these automatically to their preferred format.
41
42       Truncation is undetectable unless compressed with gzip or similar.
43
44   mboxrd
45       An evolution of "mboxo", but quotes "From " lines prefixed with any
46       number of ">" characters and is thus fully reversible.
47
48       This format is emitted by PublicInbox::WWW(3pm) with gzip.  Since git
49       2.10, "git am --patch-format=mboxrd" reads this format.  "git log" and
50       "git format-patch --stdout" can also generate this format with the
51       "--pretty=mboxrd" switch.
52
53       As with uncompressed "mboxo", uncompressed mboxrd are vulnerable to
54       undetectable truncation.
55
56       It gracefully degrades to being treated as "mboxo" by MUAs unaware of
57       the format as excessive ">From " quoting is recognizable to humans.
58
59   mboxcl
60       "mboxo" with a "Content-Length:" header, "From " lines remain quoted to
61       retain readability with "mboxo" and "mboxrd" MUAs.  However, it is easy
62       to corrupt these files when using tools which are not aware of
63       "Content-Length:" and write out updates as "mboxo".
64
65       mutt(1) will convert "mboxo" and "mboxrd" to mboxcl upon opening.
66
67       See also: <https://www.jwz.org/doc/content-length.html>
68
69   mboxcl2
70       Like "mboxcl", but without "From " any quoting.  It is wholly
71       incompatible with MUAs which only handle "mboxo" and/or "mboxrd".  This
72       is format is generated by mutt(1) when writing to a new mbox.
73

MH

75       Not yet supported, locking semantics (or lack thereof) appear to make
76       it unsuitable for parallel access.  It is widely-supported by a variety
77       of MUAs and mailing list managers, however.
78

MMDF

80       Not yet supported, and it's unclear if current usage/support makes it
81       worth supporting.
82

IMAP

84       Depending on the IMAP server software and configuration, IMAP servers
85       may use any (or combination) of the aforementioned formats or a non-
86       standard database backend.  Currently, lei uses Mail::IMAPClient which
87       has acceptable performance over low-latency links.  Performance over
88       high-latency links is currently poor.
89

eml

91       A single raw message file.  "eml" is not an output format for lei, but
92       accepted by as an "--input-format" ("-F") for read-only commands such
93       as lei-tag(1) and lei-import(1).
94
95       Since "eml" is the suffix for the "message/rfc822" MIME type (according
96       to the "mime.types" file), lei will infer the type based on the ".eml"
97       suffix if "--input-format" is unspecified
98
99       ".patch"-suffixed files generated by git-format-patch(1) (without
100       "--stdout") are "eml" files with the addition of an mbox "From "
101       header.  lei(1) removes "From " lines to treat them as "eml" when
102       reading these for compatibility with "git-am(1)" and similar tools.
103

COPYRIGHT

105       Copyright 2021 all contributors <mailto:meta@public-inbox.org>
106
107       License: AGPL-3.0+ <http://www.gnu.org/licenses/agpl-3.0.txt>
108