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Rev Author # Line
1 perry 1 mbox
2 !!!mbox
3 NAME
4 DESCRIPTION
5 LOCKING
6 FILES
7 SEE ALSO
8 AUTHOR
9 HISTORY
10 ----
11 !!NAME
12
13
14 mbox - Format for mail message storage.
15 !!DESCRIPTION
16
17
18 This document describes the format traditionally used by
19 Unix hosts to store mail messages locally. __mbox__ files
20 typically reside in the system's mail spool, under various
21 names in users' __Mail__ directories, and under the name
22 __mbox__ in users' home directories.
23
24
25 An __mbox__ is a text file containing an arbitrary number
26 of e-mail messages. Each message consists of a postmark,
27 followed by an e-mail message formatted according to RFC
28 822. The file format is line-oriented. Lines are separated
29 by line feed characters (ASCII 10).
30
31
32 A postmark line consists of the four characters
33 addrspec__ as defined in appendix
34 D of RFC 822.
35
36
37 The date is expected to be formatted according to the
38 following syntax (represented in the augmented Backus-Naur
39 formalism used by RFC 822):
40
41
42 For compatibility reasons with legacy software, two-digit years greater than or equal to 70 should be interpreted as the years 1970+, while two-digit years less than 70 should be interpreted as the years 2000-2069.
43
44
45 Software reading files in this format should also be
46 prepared to accept non-numeric timezone information such as
47
48
49 Example:
50
51
52 From roessler@does-not-exist.org Fri Jun 23 02:56:55
53 2000
54
55
56 In order to avoid mis-interpretation of lines in message
57 bodies which begin with the four characters
58 !!LOCKING
59
60
61 Since __mbox__ files are frequently accessed by multiple
62 programs in parallel, __mbox__ files should generally not
63 be accessed without locking.
64
65
66 Three different locking mechanisms (and combinations
67 thereof) are in general use:
68
69
70 fcntl(2) locking is mostly used on recent,
71 POSIX-compliant systems. Use of this locking method is, in
72 particular, advisable if __mbox__ files are accessed
73 through the Network File System (NFS), since it seems the
74 only way to reliably invalidate NFS clients'
75 caches.
76
77
78 flock(2) locking is mostly used on BSD-based
79 systems.
80
81
82 Dotlocking is used on all kinds of systems. In order to lock
83 an __mbox__ file named ''folder'', an application
84 first creates a temporary file with a unique name in the
85 directory in which the ''folder'' resides. The
86 application then tries to use the link(2) system call
87 to create a hard link named ''folder''__.lock__ to the
88 temporary file. The success of the link(2) system
89 call should be additionally verified using stat(2)
90 calls. If the link has succeeded, the mail folder is
91 considered dotlocked. The temporary file can then safely be
92 unlinked.
93
94
95 In order to release the lock, an application just unlinks
96 the ''folder''__.lock__ file.
97
98
99 If multiple methods are combined, implementors should make
100 sure to use the non-blocking variants of the fcntl(2)
101 and flock(2) sytem calls in order to avoid
102 deadlocks.
103
104
105 If multiple methods are combined, an __mbox__ file must
106 not be considered to have been successfully locked before
107 all individual locks were obtained. When one of the
108 individual locking methods fails, an application should
109 release all locks it acquired successfully, and restart the
110 entire locking procedure from the beginning, after a
111 suitable delay.
112
113
114 The locking mechanism used on a particular system is a
115 matter of local policy, and should be consistently used by
116 all applications installed on the system which access
117 __mbox__ files. Failure to do so may result in loss of
118 e-mail data, and in corrupted __mbox__
119 files.
120 !!FILES
121
122
123 /var/spool/mail/''user''
124
125
126 ''user'''s incoming mail folder.
127
128
129 ~''user''/mbox
130
131
132 ''user'''s archived mail messages, in his home
133 directory.
134
135
136 ~''user''/Mail/
137
138
139 A directory in ''user'''s home directory which is
140 commonly used to hold __mbox__ format
141 folders.
142 !!SEE ALSO
143
144
145 elm(1), fcntl(2), flock(2),
146 link(2), local(8), mail(1),
4 perry 147 maildir(5), mail.local(8), mutt(1),
148 mutt_dotlock(1), pine(1), procmail(1),
1 perry 149 sendmail(8)
150
151
152 D. Crocker, Standard for the format of ARPA Internet text
153 messages, RFC 822
154
155
156 M. R. Horton, UUCP mail interchange format standard, RFC
157 976
158 !!AUTHOR
159
160
161 The present document was written by Thomas Roessler
162 !!HISTORY
163
164
165 The __mbox__ format occured in Version 6 AT
166 __
167
168
169 A variant of this format was documented in RFC
170 976.
171 ----
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