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1 /* ========================================================================
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2 * Copyright 1988-2006 University of Washington
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3 *
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4 * Licensed under the Apache License, Version 2.0 (the "License");
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5 * you may not use this file except in compliance with the License.
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6 * You may obtain a copy of the License at
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7 *
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8 * http://www.apache.org/licenses/LICENSE-2.0
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9 *
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10 *
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11 * ========================================================================
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12 */
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13
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14 c-client Driver Characteristics
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15 Mark Crispin
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16 11 December 2006
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17
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18
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19 Drivers are code modules that support different mailbox storage
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20 technologies. A mailbox storage technology may be implemented by
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21 1) files and directories on the local system
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22 2) a database
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23 3) a network protocol.
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24
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25 In the case of files and directories on the local system, a
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26 driver supports a particular mailbox format. Mailbox formats are
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27 discussed in more detail in the file formats.txt.
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28
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29 As of the date this document was written, there was no bundled
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30 support for any databases in c-client. However, it should not be
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31 particularly difficult to write a driver that communicates with a
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32 database.
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33
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34 Network protocols supported by c-client drivers are the Internet
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35 Mail Access Protocol (all versions: IMAP4rev1, IMAP4, IMAP2bis, and
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36 IMAP2); the Post Office Protocol (version 3); and the Network News
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37 Transport Protocol (NNTP). In addition, c-client also supports NNTP
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38 and the Simple Mail Transport Protocol (SMTP) for mailbox transport.
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39
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40 By default, all drivers are enabled. There is little benefit to
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41 be gained by disabling a driver, with one exception. The mbox driver
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42 implements the behavior of automatically moving new mail from the
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43 spool directory to the "mbox" file on the user's home directory, if
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44 and *only* if the "mbox" exists and is in mailbox format. The mbox
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45 driver is listed under EXTRADRIVERS; if you wish to disable it just
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46 remove it from that list and rebuild.
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47
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48 I. Special name "INBOX"
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49
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50 The following rules to select INBOX and its format apply in
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51 the order given if "black box mode" is not in effect:
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52 1) mbox format is selected if file ~/mbox exists, and is in unix
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53 format or is zero-length.
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54 2) mx format is selected if file ~/INBOX/.mxindex exists.
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55 3) mbx format is selected if file ~/INBOX exists and is in mbx format.
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56 4) tenex format is selected if:
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57 a) file ~/mail.txt exists, and is in tenex format or is zero-length.
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58 b) file ~/INBOX exists and is in tenex format.
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59 5) mtx format is selected if:
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60 a) file ~/INBOX.MTX exists, and is in mtx format or is zero-length.
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61 b) file ~/INBOX exists and is in mtx format.
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62 6) mmdf format is selected if the spool directory file exists and is
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63 in mmdf format.
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64 7) unix format is selected if the spool directory file exists and is
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65 in unix format.
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66 8) the dummy driver is selected if the spool directory file does not
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67 exist, or exists and is empty.
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68
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69 If "black box mode" is not in effect, messages are automatically
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70 transferred ("snarfed") from the spool directory to an INBOX in mbox,
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71 mx, mbx, tenex, and mtx formats.
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72
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73 The following rules to select INBOX and its format apply in the order
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74 given if "black box mode" is in effect:
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75 1) mx format is selected if file ~/INBOX/.mxindex exists.
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76 2) mbx format is selected if file ~/INBOX exists and is in mbx format.
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77 3) tenex format is selected if file ~/INBOX exists and is in tenex format.
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78 4) mtx format is selected if file ~/INBOX exists and is in mtx format.
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79 5) mmdf format is selected if file ~/INBOX exists and is in mmdf format.
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80 6) unix format is selected if file ~/INBOX exists and is in unix format.
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81 7) the dummy driver is selected if ~/INBOX does not exist, or exists
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82 and is empty.
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83
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84 II. Special Name #mhinbox
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85
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86 #mhinbox always refers to the directory "inbox" in the MH path, which
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87 is declared in the ~/.mh_profile file. Messages are automatically
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88 transferred from the spool directory to #mhinbox mailbox.
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89
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90
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91 III. Special Prefix "#mh/"
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92
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93 Any name prefixed with "#mh/" always refers to a directory in the MH
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94 path, which is declared in the ~/.mh_profile file. For example, the name
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95 "#mh/foo" refers to directory "foo" in the MH path.
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96
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97
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98 IV. Special prefix "#news."
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99
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100 Any name prefixed with "#news" always refers to a newsgroup. For
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101 example, the name "#news.comp.mail.misc" refers to newsgroup
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102 "comp.mail.misc".
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103
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104
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105 V. All Other Names
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106
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107 The driver is selected by generating a file name from the mailbox
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108 name, and then examining the data of the object with the resulting
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109 name. The formats are checked in order: mx, mbx, tenex, mtx, mmdf,
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110 unix, and phile. The dummy driver is selected if the file is empty.
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111
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112 The file name is generated according to certain rules, based upon the
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113 prefix of the mailbox name. On UNIX, the following rules apply:
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114
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115 Prefix Interpretation of Suffix
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116 ------ ------------------------
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117 / [black box] preceeds a user name; "/foo/bar" means
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118 "black box user foo's mailbox bar"
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119 [not black box] preceeds an absolute path name.
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120 ~ [not black box] preceeds a user name; "~foo/bar" means
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121 "UNIX user foo's mailbox bar"
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122 #ftp/ preceeds UNIX user ftp's mailbox name
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123 #public/ preceeds UNIX user imappublic's mailbox name
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124 #shared/ preceeds UNIX user imapshared's mailbox name
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125
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126 All other names are interpreted in the context of the UNIX user's home
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127 directory (not black box), the black box user's black box directory
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128 (black box), or UNIX user ftp's home directory (anonymous).
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129
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130 The strings "..", "//", and /~ are forbidden in names in:
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131 black box mode
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132 #ftp, #public, or #shared names
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133 anonymous users
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134
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135 Anonymous users may only access:
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136 INBOX (belonging to UNIX user ftp)
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137 files in or below UNIX user ftp's home directory
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138 #ftp, #news, and #public namespace
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139
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140 VI. Driver Comparison
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141
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142 The following information about the local file drivers is an
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143 elaboration of a table compiled by Osma Ahvenlampi.
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144
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145 Driver CA CE UID Kwd Sub NFS Performance Layout
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146 ------ -- -- --- --- --- --- ----------- ------
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147 unix no no yes yes no limited fair file
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148 ;;; traditional UNIX format
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149 mbox no no yes yes no limited fair file
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150 ;;; traditional UNIX format, INBOX only, using ~/mbox with automatic
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151 ;;; moving from the mail spool directory.
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152 mmdf no no yes yes no limited fair file
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153 ;;; default on SCO systems
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154 mbx yes yes yes yes no no very good prefile
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155 ;;; best performing local file driver; preferred format at UW
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156 tenex yes no no limited no no good prefile
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157 ;;; compatible with UNIX MM
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158 mtx yes no no limited no no very good prefile
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159 ;;; PC Pine standard format; compatible with TOPS-20; identical to tenex
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160 ;;; but instead CRLF newlines instead of LF
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161 mx yes buggy yes yes yes no poor ixdir
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162 ;;; fullest function; *not* recommended due to performance problems and bugs;
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163 ;;; to be redesigned/rewritten
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164 mh yes no no no yes yes very poor dir
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165 ;;; compatible with mh; #mhinbox for INBOX, #mh/ prefix for all other names
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166 news yes no yes no yes yes very poor ixdir
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167 ;;; local news spool access; #news. prefix for all names
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168 phile no no no no no yes good file
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169 ;;; reads arbitrary file as a single readonly message
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170
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171 IMPORTANT: the "performance" ratings are relative to other drivers,
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172 and not necessarily to other software which implements those formats.
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173 They relate to the driver's performance in typical operations such as
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174 an IMAP "FETCH ALL".
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175
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176 Key to headings:
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177 CA: concurrent read/write access
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178 CE: expunge permitted in concurrent read/write access
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179 UID: sticky UIDs
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180 Kwd: keyword flags
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181 Sub: subfolders
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182 NFS: usable over network filesystems (NFS, AFS, etc.)
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183 Layout: file - single file
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184 prefile - file with preallocated space for state
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185 dir - directory, messages are files
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186 ixdir - directory, messages are files, with helper index
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187
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188 In addition, drivers imap, nntp, and pop3 support IMAP4rev1, NNTP, and
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189 POP3 protocols respectively.
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