954:
overwrite existing mails.¶ Step 2 is pointless because there's a race condition between steps 2 and 3. PID/host combination by itself should already guarantee that it never finds such a file. If it does, something's broken and the stat() check won't help since another process might be doing the same thing at the same time, and you end up writing to the same file in tmp/, causing the mail to get corrupted.¶ In step 4 the link() would fail if an identical file already existed in the
Maildir, right? Wrong. The file may already have been moved to cur/ directory, and since it may contain any number of flags by then you can't check with a simple stat() anymore if it exists or not.¶ Step 2 was pointed out to be useful if clock had moved backwards. However, this doesn't give any actual safety guarantees because an identical base filename could already exist in cur/. Besides if the system was just rebooted, the file in tmp/ could probably be even overwritten safely (assuming it wasn't already link()ed to new/).¶ So really, all that's important in not getting mails overwritten in your Maildir is step 1: Always create filenames that are guaranteed to be unique. Forget about the 2 second waits and such that the Qmail's man page talks about.
477:. The "2" specifies the version of the information that follows the comma. "2" is the only currently officially specified version, "1" being an experimental version. The specification defines flags that show whether the message has been read, deleted and so on: the initial (capital) letter of "Passed", "Replied", "Seen", "Trashed", "Draft", and "Flagged". Applications often choose to supplement this very limited set of flags, for example notmuch offers flag synchronization in addition to arbitrary user-defined flags, while Dovecot uses lowercase letters to match 26 IMAP keywords, which may include keywords such as $
953:
All this trouble is rather pointless. Only the first step is what really guarantees that the mails won't get overwritten, the rest just sounds nice. Even though they might catch a problem once in a while, they give no guaranteed protection and will just as easily pass duplicate filenames through and
118:
extension to the
Maildir format to support subfolders and mail quotas. Maildir++ directories contain subdirectories with names that start with a '.' (dot) which are also Maildir++ folders. The extension complies with the original Maildir specification, which allows for subdirectories in addition to
42:
circa 1995, with a major goal of eliminating the need for program code to handle file locking and unlocking through use of the local filesystem. Maildir design reflects the fact that the only operations valid for an email message is that it be created, deleted or have its status changed in some way.
205:
By 2003, the recommendations had been further amended to require that instead of the PID and counter, the middle part of the filename should be created by "concatenating enough of the following strings to guarantee uniqueness" even in the face of multiple simultaneous deliveries to the same maildir
510:
As there is currently no agreement on what character this alternative separator should be, there can be interoperability difficulties between different
Maildir-supporting programs on these systems. However, not all Maildir-related software needs to know what the separator character is, because not
511:
all
Maildir-related software needs to be able to read or modify the flags of a message ("read", "replied to" etc.); software that merely delivers to a Maildir or archives old messages from it based only on date, should work no matter what separator is in use. If only the
295:
is (in hexadecimal) the UNIX device number of this file. Unfortunately, device numbers aren't always available through NFS. (Device numbers are also not helpful with the standard UNIX filesystem: a maildir has to be within a single UNIX device for
201:
By 2000, the qmail author recommended in an updated specification to append the value of a per-process counter to the PID, whose value should be incremented after each delivery. The rate-limiting recommendation to "wait two seconds" was dropped.
406:. Any leftover file will eventually be deleted. This sequence guarantees that a maildir-reading program will not see a partially written message. There can be multiple programs reading a maildir at the same time. They range from
238:
system call, which reports the number of times that the system has been booted. Together with #, this guarantees uniqueness; unfortunately, most operating systems don't support
87:
subdirectory temporarily stores e-mail messages that are in the process of being delivered. This subdirectory may also store other kinds of temporary files.
941:
515:
needs to read or modify message flags, and only one MUA is used, then non-standard alternative separators may be used without interoperability problems.
1093:
465:
technique is non-atomic and may result in duplicated messages. An informational suffix is appended to filenames at this stage. It consists of a
782:
834:
746:
484:
Although
Maildir was intended to allow lockless usage, in practice some software that uses Maildirs also uses locks, such as Dovecot.
1061:
478:
438:
411:
47:
1260:
772:
504:
147:
that delivers an email message into a
Maildir. The mail delivery agent creates a new file with a unique filename in the
808:
583:
38:
with a unique name, and each mail folder is a file system directory containing these files. Maildir was designed by
1223:
912:
1011:
866:
60:
937:
223:
system call, which returns a number that increases by 1 every time it is called, starting from 0 after reboot.
151:
directory. At the time of its invention guaranteeing unique filenames efficiently was difficult. The original
500:
94:
subdirectory stores messages that have been delivered, but have not yet been seen by any mail application.
1089:
981:
713:
666:
361:
had made no further changes to the 2003 filename generation recommendations. On modern POSIX systems,
678:
672:
434:
415:
965:
904:
858:
742:
718:
705:
590:
537:
524:
466:
358:
281:
140:
111:
39:
602:
555:
531:
503:) can use a non-standard alternative separator, such as ";" or "-". It is often trivial to patch
390:
351:
186:
166:
1137:
889:
1240:
778:
496:
265:. Unfortunately, some operating systems don't include cryptographic random number generators.
474:
144:
1191:
830:
750:
969:
656:
492:
The
Maildir standard can only be implemented on systems that accept colons in filenames.
407:
985:
622:
426:, which may or may not be aware of the maildir structure. Readers should never look in
362:
1254:
1085:
933:
347:
197:
create a file with the unique filename and write the message contents to the new file
35:
469:(to separate the unique part of the filename from the actual information), a "2", a
512:
374:
The delivery process stores the message in the maildir by creating and writing to
280:
number of this file. Unfortunately, inode numbers aren't always available through
1114:
1228:
637:
419:
31:
101:
subdirectory stores messages that have already been seen by mail applications.
346:
This 2003 algorithm was criticised in 2006 as being unnecessarily complex by
617:
573:
395:
179:
160:
721:– experimental and “disabled by default because there are still many bugs”
804:
1138:
mutt maildir support: workaround for filesystems that don't accept colons
608:
597:
543:
173:
457:
new messages". This moving needs to be done using the atomic filesystem
684:
648:
613:
367:
998:
That specification requires that the action of the function be atomic.
1245:
908:
862:
23:
394:, which is atomic in many systems. Alternatively, it can be done by
616:, a Maildir-aware mail-retrieval and delivery agent alternative to
441:
server, or a mail user agent acting locally) finds messages in the
46:
700:
694:
567:
561:
470:
423:
277:
178:
concatenate the above three values into a string separated by the
152:
27:
540:
SMTP and IMAP server, for which the
Maildir++ format was invented
1218:
689:
642:
549:
410:(MUAs), which access the server's file system directly, through
669:
previously the official GNOME mail reader (prior to
Evolution)
418:
servers acting on behalf of remote MUAs, to utilities such as
341:
is (in decimal) the number of deliveries made by this process.
627:
495:
Systems that don't allow colons in filenames (this includes
1167:
1037:
631:
1149:
257:
is (in hexadecimal) the output of the operating system's
234:
is (in hexadecimal) the output of the operating system's
219:
is (in hexadecimal) the output of the operating system's
710:
Notmuch (fast, global-search and tag-based email system)
34:, rather than in a database. Each message is assigned a
191:
reports that the filename exists, then wait two seconds
645:, synchronises mailboxes, supporting Maildir and IMAP4
564:
SMTP server, for which the
Maildir format was invented
315:
is (in decimal) the microsecond counter from the same
579:
194:
go to previous step until the filename does not exist
651:, a minimal Maildir-aware MDA implemented in Haskell
1115:"mailbox — Manipulate mailboxes in various formats"
453:. It is just a means to notify the user "you have
433:When a cognizant maildir-reading process (either a
798:
796:
794:
1150:"aerc - the world's best email client homepage"
737:
735:
899:
897:
853:
851:
261:system call or an equivalent source, such as
8:
663:aerc (efficient and extensible email client)
319:used for the left part of the unique name.
885:
883:
67:) usually has three subdirectories named
938:"Maildir Mailbox Format: Mail Delivery'"
634:mailboxes between any number of replicas
45:
731:
519:Software that supports Maildir directly
582:, SMTP and IMAP server implemented in
7:
110:Sam Varshavchik, the author of the
1012:"Management of maildir structures"
357:As of November 2023, qmail author
26:format is a common way of storing
14:
1090:"Maildir Mailbox Format: Locking"
402:and then unlinking the file from
1010:Sam Varshavchik (25 July 2016).
488:File-system compatibility issues
412:Internet Message Access Protocol
155:algorithm for unique names was:
114:and other software, defined the
1096:from the original on 2024-06-24
944:from the original on 2024-06-24
915:from the original on 2003-04-01
869:from the original on 2000-09-02
837:from the original on 2024-05-29
811:from the original on 2024-04-17
388:. The moving can be done using
381:, and then moving this file to
365:can be safely created with the
330:is (in decimal) the process ID.
1168:"Notmuch mail system homepage"
1062:"notmuch 0.38.3 documentation"
1038:"Notmuch mail system homepage"
507:to use a different separator.
1:
505:free and open-source software
276:is (in hexadecimal) the UNIX
890:Dovecot Wiki: maildir format
681:, official GNOME mail client
206:from one or more processes:
499:and some configurations of
1277:
1224:MH Message Handling System
675:a curses-based mail reader
182:; this is the new filename
829:Varshavchik, Sam (2011).
803:Varshavchik, Sam (2009).
259:unix_cryptorandomnumber()
1192:"Maildir in Thunderbird"
546:The original SMTP server
1241:manual page for maildir
501:Novell Storage Services
481:or user-defined flags.
1246:maildir specifications
909:"Using maildir format"
863:"Using maildir format"
771:Blum, Richard (2001).
344:
51:
1261:Email storage formats
905:Bernstein., Daniel J.
859:Bernstein., Daniel J.
461:, as the alternative
240:unix_sequencenumber()
221:unix_sequencenumber()
208:
49:
1119:Python documentation
743:Bernstein, Daniel J.
726:Notes and references
580:Stalwart Mail Server
416:Post Office Protocol
371:C library function.
777:. Sams Publishing.
719:Mozilla Thunderbird
538:Courier Mail Server
141:mail delivery agent
135:Technical operation
112:Courier Mail Server
40:Daniel J. Bernstein
167:process identifier
52:
50:Internal structure
784:978-0-672-32114-6
697:, KDE mail reader
497:Microsoft Windows
350:, the creator of
244:unix_bootnumber()
236:unix_bootnumber()
172:read the current
165:read the current
159:read the current
1268:
1206:
1205:
1203:
1202:
1188:
1182:
1181:
1179:
1178:
1164:
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1135:
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1125:
1111:
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1104:
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1073:
1072:
1058:
1052:
1051:
1049:
1048:
1034:
1028:
1027:
1025:
1023:
1007:
1001:
1000:
995:
993:
978:
972:
963:
957:
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950:
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924:
923:
921:
920:
901:
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878:
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843:
842:
826:
820:
819:
817:
816:
800:
789:
788:
768:
762:
761:
759:
758:
749:. Archived from
739:
630:, synchronising
463:link-then-unlink
460:
452:
444:
429:
408:mail user agents
405:
401:
393:
387:
380:
370:
359:Daniel Bernstein
318:
303:
299:
264:
260:
245:
241:
237:
222:
189:
180:period character
150:
100:
93:
86:
78:
74:
70:
66:
1276:
1275:
1271:
1270:
1269:
1267:
1266:
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1251:
1250:
1237:
1215:
1210:
1209:
1200:
1198:
1190:
1189:
1185:
1176:
1174:
1172:notmuchmail.org
1166:
1165:
1161:
1148:
1147:
1143:
1136:
1132:
1123:
1121:
1113:
1112:
1108:
1099:
1097:
1084:
1083:
1079:
1070:
1068:
1060:
1059:
1055:
1046:
1044:
1042:notmuchmail.org
1036:
1035:
1031:
1021:
1019:
1009:
1008:
1004:
991:
989:
980:
979:
975:
970:Wayback Machine
964:
960:
947:
945:
932:
931:
927:
918:
916:
903:
902:
895:
888:
881:
872:
870:
857:
856:
849:
840:
838:
828:
827:
823:
814:
812:
802:
801:
792:
785:
770:
769:
765:
756:
754:
741:
740:
733:
728:
660:
594:
591:Delivery agents
528:
521:
490:
458:
450:
442:
427:
403:
399:
389:
382:
375:
366:
363:temporary files
316:
301:
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262:
258:
243:
239:
235:
220:
187:
148:
137:
108:
98:
91:
84:
76:
72:
68:
64:
57:
17:
12:
11:
5:
1274:
1272:
1264:
1263:
1253:
1252:
1249:
1248:
1243:
1236:
1235:External links
1233:
1232:
1231:
1226:
1221:
1214:
1211:
1208:
1207:
1183:
1159:
1141:
1130:
1106:
1086:Sirainen, Timo
1077:
1066:notmuch-config
1053:
1029:
1018:(Mailing list)
1002:
986:The Open Group
973:
958:
934:Sirainen, Timo
925:
893:
879:
847:
821:
790:
783:
763:
730:
729:
727:
724:
723:
722:
716:
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620:
611:
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605:delivery agent
600:
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577:
571:
565:
559:
553:
547:
541:
535:
527:
522:
520:
517:
489:
486:
445:directory, it
385:uniquefilename
378:uniquefilename
343:
342:
331:
320:
317:gettimeofday()
305:
285:
266:
247:
224:
199:
198:
195:
192:
183:
176:
170:
163:
136:
133:
107:
104:
103:
102:
95:
88:
56:
55:Specifications
53:
30:messages on a
15:
13:
10:
9:
6:
4:
3:
2:
1273:
1262:
1259:
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1160:
1155:
1154:aerc-mail.org
1151:
1145:
1142:
1139:
1134:
1131:
1120:
1116:
1110:
1107:
1095:
1091:
1087:
1081:
1078:
1067:
1063:
1057:
1054:
1043:
1039:
1033:
1030:
1017:
1016:courier-users
1013:
1006:
1003:
999:
987:
983:
977:
974:
971:
967:
966:Archive index
962:
959:
955:
943:
939:
935:
929:
926:
914:
910:
906:
900:
898:
894:
891:
886:
884:
880:
868:
864:
860:
854:
852:
848:
836:
832:
825:
822:
810:
806:
799:
797:
795:
791:
786:
780:
776:
775:
767:
764:
753:on 1997-10-12
752:
748:
744:
738:
736:
732:
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704:
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610:
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581:
578:
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551:
548:
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536:
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530:
529:
526:
523:
518:
516:
514:
508:
506:
502:
498:
493:
487:
485:
482:
480:
476:
472:
468:
464:
456:
449:move them to
448:
440:
436:
431:
425:
421:
417:
413:
409:
397:
392:
386:
379:
372:
369:
364:
360:
355:
353:
349:
348:Timo Sirainen
340:
336:
332:
329:
325:
321:
314:
310:
306:
294:
290:
286:
283:
279:
275:
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117:
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105:
96:
89:
82:
81:
80:
63:(often named
62:
54:
48:
44:
41:
37:
33:
29:
25:
22:
16:E-mail format
1199:. Retrieved
1195:
1186:
1175:. Retrieved
1171:
1162:
1153:
1144:
1133:
1122:. Retrieved
1118:
1109:
1098:. Retrieved
1080:
1069:. Retrieved
1065:
1056:
1045:. Retrieved
1041:
1032:
1020:. Retrieved
1015:
1005:
997:
990:. Retrieved
976:
961:
952:
946:. Retrieved
928:
917:. Retrieved
871:. Retrieved
861:(c. 2000) .
839:. Retrieved
824:
813:. Retrieved
805:"maildir(5)"
773:
766:
755:. Retrieved
751:the original
747:"maildir(5)"
657:Mail readers
632:notmuch mail
525:Mail servers
509:
494:
491:
483:
473:and various
462:
454:
446:
432:
398:the file to
396:hard-linking
384:
377:
373:
356:
345:
338:
334:
327:
323:
312:
308:
292:
288:
273:
269:
263:/dev/urandom
254:
250:
231:
227:
216:
212:
204:
200:
138:
128:
124:
120:
115:
109:
58:
20:
18:
1229:MIX (email)
1196:mozilla.org
831:"Maildir++"
714:Pine/Alpine
638:OfflineIMAP
576:SMTP server
570:SMTP server
558:SMTP server
552:SMTP server
534:IMAP server
32:file system
1201:2020-12-06
1177:2019-06-22
1124:2023-06-19
1100:2024-08-09
1071:2024-04-17
1047:2019-06-22
948:2024-08-09
919:2018-11-23
873:2018-11-23
841:2024-08-09
815:2024-08-09
757:2018-11-23
59:A Maildir
907:(2003) .
679:Evolution
618:Fetchmail
574:OpenSMTPD
304:to work.)
161:Unix time
116:Maildir++
106:Maildir++
61:directory
1255:Category
1213:See also
1094:Archived
982:"rename"
942:Archived
913:Archived
867:Archived
835:Archived
809:Archived
745:(1995).
649:Attomail
628:muchsync
609:maildrop
598:procmail
544:Sendmail
459:rename()
337:, where
326:, where
311:, where
302:rename()
291:, where
272:, where
253:, where
230:, where
215:, where
174:hostname
1022:26 July
992:23 July
968:at the
774:Postfix
685:GNUMail
614:getmail
603:Dovecot
556:Postfix
532:Dovecot
479:MDNSent
368:mkstemp
352:Dovecot
145:program
65:Maildir
21:Maildir
988:. 2013
781:
391:rename
298:link()
188:stat()
75:, and
24:e-mail
701:mailx
695:KMail
667:Balsa
643:isync
568:MeTA1
562:qmail
475:flags
471:comma
467:colon
424:rsync
278:inode
169:(PID)
153:qmail
143:is a
28:email
1219:mbox
1024:2016
994:2016
779:ISBN
706:Mutt
690:Gnus
673:Cone
584:Rust
550:Exim
447:must
439:IMAP
422:and
420:biff
383:new/
376:tmp/
300:and
242:and
127:and
97:The
90:The
83:The
36:file
19:The
623:fdm
513:MUA
451:cur
443:new
437:or
435:POP
428:tmp
414:or
404:tmp
400:new
282:NFS
185:if
149:tmp
129:cur
125:new
121:tmp
99:cur
92:new
85:tmp
79:.
77:cur
73:new
69:tmp
1257::
1194:.
1170:.
1152:.
1117:.
1092:.
1088:.
1064:.
1040:.
1014:.
996:.
984:.
951:.
940:.
936:.
911:.
896:^
882:^
865:.
850:^
833:.
807:.
793:^
734:^
430:.
354:.
139:A
131:.
123:,
71:,
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