Mercurial > dovecot > core-2.2
annotate doc/mail-storages.txt @ 1741:9df02b1533b3 HEAD
Removed most of the license comments from src/lib/*.c. It's just fine to
keep them in a single COPYING.MIT file. Changed a few other comments as well.
| author | Timo Sirainen <tss@iki.fi> |
|---|---|
| date | Wed, 27 Aug 2003 00:18:16 +0300 |
| parents | 19ef482ece51 |
| children | 1f92f41addea |
| rev | line source |
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| 430 | 1 Maildir |
| 2 ------- | |
| 429 | 3 |
| 4 We support Courier-compatible Maildir++. INBOX is the ~/Maildir directory, | |
| 5 all the other folders named as ".<folder>.<subfolder>.<etc>" under it, any | |
| 6 directories not starting with a dot are simply ignored. Deleting folders is | |
| 7 made atomic by renaming them as "..<folder name>" and deleting the | |
| 8 directory after that. So, all directories beginning with ".." are deleted | |
| 9 whenever they're noticed. Indexes are stored into each folder's root | |
| 10 directory. | |
| 11 | |
| 12 Custom flags saved using a..z letters as Maildir file flags. .customflags | |
| 13 file is then used to map the letters to names (a=0, b=1, etc). | |
| 14 | |
| 430 | 15 |
| 16 mbox | |
| 17 ---- | |
| 429 | 18 |
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19 mbox storage requires an IMAP root directory where to store IMAP folders |
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20 and some other information. mbox file for INBOX is a special case which may |
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21 exist elsewhere in filesystem. |
| 429 | 22 |
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23 All files in the IMAP root directory not beginning with a "." are treated |
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24 as IMAP folders. Directories are treated as being IMAP subfolders. |
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25 |
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26 Dovecot's indexes are stored in ".imap/<mailbox name>/" directories under |
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27 the folder directories. |
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28 |
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29 MAIL environment for mbox is: <root folder>|<INBOX path>[:INBOX=<path>]. |
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30 For example ~/Mail:INBOX=/var/mail/username. |
| 430 | 31 |
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32 indexes |
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33 ------- |
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34 |
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35 It's possible to specify different location for index files. This could be |
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36 wanted if mailboxes are accessed via remote filesystem (eg. NFS). Indexes |
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37 are mmap()ed and fcntl() locked, so they may not work too well with NFS, or |
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38 at least they'll work a bit slowly. |
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39 |
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40 Indexes don't contain anything really important in them, so it doesn't |
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41 matter if they're lost or are out of sync. Dovecot just rebuilds or |
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42 refreshes them. This would allow creating a cluster where each computer |
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43 keeps the indexes locally while accessing the actual mailboxes via NFS. To |
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44 avoid unnecessarily rebuilding indexes all the time, the users should be |
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45 redirected to their primary server whenever possible. |
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46 |
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47 Currently the only annoying thing with recreating indexes is that the |
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48 message UIDs will change, which may cause more traffic to clients, and |
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49 depending on client software may cause loss of some message-specific |
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50 settings. This will be fixed later by storing the UIDs permanently to |
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51 mailboxes. |
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52 |
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53 Adding :INDEX=<dir> to MAIL environment overrides the default location. The |
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54 given directory must exist. |
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55 |
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56 It's also possible to disable index files by building them into memory. |
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57 They're also automatically built into memory if the index files can't be |
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58 opened or created for some reason (eg. out of disk space). To disable |
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59 indexes always, add :INDEX=MEMORY to MAIL environment. |
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60 |
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61 |
| 430 | 62 Detecting what to use |
| 63 --------------------- | |
| 429 | 64 |
| 65 imap process detects the storage from MAIL-environment. It's preferred | |
| 66 format is "<storage>:<data>", for example "maildir:~/Maildir". It's anyway | |
| 67 allowed to be in pretty much any format as long as some of the storages | |
| 68 recognizes it as a valid data, so for example "MAIL=~/mail" is first | |
| 69 checked by maildir storage to see if it's valid maildir and mbox storage | |
| 70 after that. | |
| 71 | |
| 72 If the MAIL environment isn't given at all, all storages are gone through | |
| 73 and asked if they can find a usable mail folder. Also as a special case, if | |
| 74 MAILDIR environment exists, maildir storage is used with the directory | |
| 75 specified in it. | |
| 76 | |
| 77 Maildir storage is autodetected by checking if <directory>/cur/ exists and | |
| 78 we have rwx access to it. If directory isn't known, / and ~/Maildir are | |
| 79 checked. / is checked because we could be chrooted. | |
| 80 | |
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81 mbox storage requires detecting INBOX location and IMAP root directory. If |
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82 MAIL environment points to file (+rw) it's treated as the INBOX file. If it |
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83 points to directory (+rwx) which contains .imap/ (+rwx), inbox (+rw) or |
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84 mbox (+rw) it's treated as IMAP root directory. If INBOX isn't known, |
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85 imap_root/inbox file is used by default. If root directory isn't known, we |
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86 try to find it from /, ~/mail or ~/Mail. |
| 429 | 87 |
| 430 | 88 |
| 89 Files created by Dovecot | |
| 90 ------------------------ | |
| 429 | 91 |
| 92 .subscriptions: One folder per line listing subscribed IMAP folders. | |
| 93 There's only one of these files in the root mail directory (~/Maildir/ or | |
| 94 ~/mail/.imap/). | |
| 95 | |
| 96 Then there's the per-folder files: | |
| 97 | |
| 98 .imap.index: Fixed width mail index records. | |
| 99 | |
| 100 .imap.index.data: Variable width data, for example mail file name and | |
| 101 cached body, envelope, etc. | |
| 102 | |
| 103 .imap.index.log: Log file describing made changes. This file is used to | |
| 104 mark external changes (expunges and flag changes) temporarily until they're | |
| 105 synced into IMAP clients. If multiple Dovecots have the same folder open, | |
| 106 this can be a big speedup. | |
| 107 | |
| 108 .imap.index.tree: Binary tree used for looking up messages from .imap.index | |
| 109 file. This is used for both UID lookups and message sequence lookups. | |
| 110 Sequences can be looked up directly from the index as long as no messages | |
| 111 have been expunged, but after that it gets slow unless it's compressed. | |
| 112 Using this file however can keep the sequence lookups and expunges fast in | |
| 113 all situations without requiring compression. | |
| 114 | |
| 115 .customflags: Lists custom message flags. First line is header which | |
| 116 Dovecots check to see if the file has changed. Other lines list the flags | |
| 117 in format "<flag number> <flag name>". Currently there can be 26 different | |
| 118 flags (0..25). | |
| 119 | |
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120 .imap.index* files can be deleted without any data loss, they're simply |
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121 recreated/rebuilt when they're noticed missing. |
| 429 | 122 |
| 123 Deleting .customflags results in loss of custom flag names for Maildir. | |
| 124 With mbox the .customflags is simply recreated based on the flags listed | |
| 125 in the mbox file itself (ie. no data loss). |