diff options
Diffstat (limited to 'upstream/debian-unstable/man5/maildir.maildrop.5')
| -rw-r--r-- | upstream/debian-unstable/man5/maildir.maildrop.5 | 354 |
1 files changed, 354 insertions, 0 deletions
diff --git a/upstream/debian-unstable/man5/maildir.maildrop.5 b/upstream/debian-unstable/man5/maildir.maildrop.5 new file mode 100644 index 00000000..c0b9e1b9 --- /dev/null +++ b/upstream/debian-unstable/man5/maildir.maildrop.5 @@ -0,0 +1,354 @@ +'\" t +.\"<!-- Copyright 1998 - 2007 Double Precision, Inc. See COPYING for --> +.\"<!-- distribution information. --> +.\" Title: maildir +.\" Author: Sam Varshavchik +.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/> +.\" Date: 07/24/2017 +.\" Manual: Double Precision, Inc. +.\" Source: Courier Mail Server +.\" Language: English +.\" +.TH "MAILDIR" "5" "07/24/2017" "Courier Mail Server" "Double Precision, Inc\&." +.\" ----------------------------------------------------------------- +.\" * Define some portability stuff +.\" ----------------------------------------------------------------- +.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +.\" http://bugs.debian.org/507673 +.\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html +.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +.ie \n(.g .ds Aq \(aq +.el .ds Aq ' +.\" ----------------------------------------------------------------- +.\" * set default formatting +.\" ----------------------------------------------------------------- +.\" disable hyphenation +.nh +.\" disable justification (adjust text to left margin only) +.ad l +.\" ----------------------------------------------------------------- +.\" * MAIN CONTENT STARTS HERE * +.\" ----------------------------------------------------------------- +.SH "NAME" +maildir \- E\-mail directory +.SH "SYNOPSIS" +.sp +$HOME/Maildir +.SH "DESCRIPTION" +.PP +A +\(lqMaildir\(rq +is a structured directory that holds E\-mail messages\&. Maildirs were first implemented by the +Qmail +mail server\&. Qmail\*(Aqs maildirs were a simple data structure, nothing more than a single collection of E\-mail messages\&. The +Courier +mail server builds upon +Qmail\*(Aqs maildirs to provide extended functionality, such as folders and quotas\&. This document describes the +Courier +mail server\*(Aqs extended maildirs, without explicitly identifying The +Courier +mail server\-specific extensions\&. See +\fBmaildir\fR(5) +in Qmail\*(Aqs documentation for the original definition of maildirs\&. +.PP +Traditionally, E\-mail folders were saved as plain text files, called +\(lqmboxes\(rq\&. Mboxes have known limitations\&. Only one application can use an mbox at the same time\&. Locking is required in order to allow simultaneous concurrent access by different applications\&. Locking is often problematic, and not very reliable in network\-based filesystem requirements\&. Some network\-based filesystems don\*(Aqt offer any reliable locking mechanism at all\&. Furthermore, even bulletproof locking won\*(Aqt prevent occasional mbox corruption\&. A process can be killed or terminated in the middle of updating an mbox\&. This will likely result in corruption, and a loss of most messages in the mbox\&. +.PP +Maildirs allow multiple concurrent access by different applications\&. Maildirs do not require locking\&. Multiple applications can update a maildir at the same time, without stepping on each other\*(Aqs feet\&. +.SS "Maildir contents" +.PP +A +\(lqmaildir\(rq +is a directory that\*(Aqs created by +\m[blue]\fB\fBmaildirmake\fR(1)\fR\m[]\&\s-2\u[1]\d\s+2\&. Naturally, maildirs should not have any group or world permissions, unless you want other people to read your mail\&. A maildir contains three subdirectories: +tmp, +new, and +cur\&. These three subdirectories comprise the primary folder, where new mail is delivered by the system\&. +.PP +Folders are additional subdirectories in the maildir whose names begin with a period: such as +\&.Drafts +or +\&.Sent\&. Each folder itself contains the same three subdirectories, +tmp, +new, and +cur, and an additional zero\-length file named +maildirfolder, whose purpose is to inform any mail delivery agent that it\*(Aqs really delivering to a folder, and that the mail delivery agent should look in the parent directory for any maildir\-related information\&. +.PP +Folders are not physically nested\&. A folder subdirectory, such as +\&.Sent +does not itself contain any subfolders\&. The main maildir contains a single, flat list of subfolders\&. These folders are logically nested, and periods serve to separate folder hierarchies\&. For example, +\&.Sent\&.2002 +is considered to be a subfolder called +\(lq2002\(rq +which is a subfolder of +\(lqSent\(rq\&. +.sp +.it 1 an-trap +.nr an-no-space-flag 1 +.nr an-break-flag 1 +.br +.ps +1 +\fBFolder name encoding\fR +.RS 4 +.PP +Folder names can contain any Unicode character, except for control characters\&. US\-ASCII characters, U+0x0020 \- U+0x007F, except for the period, forward\-slash, and ampersand characters (U+0x002E, U+0x002F, and U+0x0026) represent themselves\&. The ampersand is represent by the two character sequence +\(lq&\-\(rq\&. The period, forward slash, and non US\-ASCII Unicode characters are represented using the UTF\-7 character set, and encoded with a modified form of base64\-encoding\&. +.PP +The +\(lq&\(rq +character starts the modified base64\-encoded sequence; the sequence is terminated by the +\(lq\-\(rq +character\&. The sequence of 16\-bit Unicode characters is written in big\-endian order, and encoded using the base64\-encoding method described in section 5\&.2 of +\m[blue]\fBRFC 1521\fR\m[]\&\s-2\u[2]\d\s+2, with the following modifications: +.sp +.RS 4 +.ie n \{\ +\h'-04'\(bu\h'+03'\c +.\} +.el \{\ +.sp -1 +.IP \(bu 2.3 +.\} +The +\(lq=\(rq +padding character is omitted\&. When decoding, an incomplete 16\-bit character is discarded\&. +.RE +.sp +.RS 4 +.ie n \{\ +\h'-04'\(bu\h'+03'\c +.\} +.el \{\ +.sp -1 +.IP \(bu 2.3 +.\} +The comma character, +\(lq,\(rq +is used in place of the +\(lq/\(rq +character in the base64 alphabet\&. +.RE +.PP +For example, the word +\(lqResume\(rq +with both "e"s being the e\-acute character, U+0x00e9, is encoded as +\(lqR&AOk\-sum&AOk\-\(rq +(so a folder of that name would be a maildir subdirectory called +\(lq\&.R&AOk\-sum&AOk\-\(rq)\&. +.RE +.sp +.it 1 an-trap +.nr an-no-space-flag 1 +.nr an-break-flag 1 +.br +.ps +1 +\fBOther maildir contents\fR +.RS 4 +.PP +Software that uses maildirs may also create additional files besides the +tmp, +new, and +cur +subdirectories \-\- in the main maildir or a subfolder \-\- for its own purposes\&. +.RE +.SS "Messages" +.PP +E\-mail messages are stored in separate, individual files, one E\-mail message per file\&. The +tmp +subdirectory temporarily stores E\-mail messages that are in the process of being delivered to this maildir\&. +tmp +may also store other kinds of temporary files, as long as they are created in the same way that message files are created in +tmp\&. The +new +subdirectory stores messages that have been delivered to this maildir, but have not yet been seen by any mail application\&. The +cur +subdirectory stores messages that have already been seen by mail applications\&. +.SS "Adding new mail to maildirs" +.PP +The following process delivers a new message to the maildir: +.PP +A new unique filename is created using one of two possible forms: +\(lqtime\&.MusecPpid\&.host\(rq, or +\(lqtime\&.MusecPpid_unique\&.host\(rq\&. +\(lqtime\(rq +and +\(lqusec\(rq +is the current system time, obtained from +\fBgettimeofday\fR(2)\&. +\(lqpid\(rq +is the process number of the process that is delivering this message to the maildir\&. +\(lqhost\(rq +is the name of the machine where the mail is being delivered\&. In the event that the same process creates multiple messages, a suffix unique to each message is appended to the process id; preferrably an underscore, followed by an increasing counter\&. This applies whether messages created by a process are all added to the same, or different, maildirs\&. This protocol allows multiple processes running on multiple machines on the same network to simultaneously create new messages without stomping on each other\&. +.PP +The filename created in the previous step is checked for existence by executing the +\fBstat\fR(2) +system call\&. If +\fBstat\fR(2) +results in ANYTHING OTHER than the system error +ENOENT, the process must sleep for two seconds, then go back and create another unique filename\&. This is an extra step to insure that each new message has a completely unique filename\&. +.PP +Other applications that wish to use +tmp +for temporary storage should observe the same protocol (but see READING MAIL FROM MAILDIRS below, because old files in +tmp +will be eventually deleted)\&. +.PP +If the +\fBstat\fR(2) +system call returned +ENOENT, the process may proceed to create the file in the +tmp +subdirectory, and save the entire message in the new file\&. The message saved MUST NOT have the +\(lqFrom_\(rq +header that is used to mboxes\&. The message also MUST NOT have any +\(lqFrom_\(rq +lines in the contents of the message prefixed by the +\(lq>\(rq +character\&. +.PP +When saving the message, the number of bytes returned by the +\fBwrite\fR(2) +system call must be checked, in order to make sure that the complete message has been written out\&. +.PP +After the message is saved, the file descriptor is +\fBfstat\fR(2)\-ed\&. The file\*(Aqs device number, inode number, and the its byte size, are saved\&. The file is closed and is then immediately moved/renamed into the +new +subdirectory\&. The name of the file in +new +should be +\(lqtime\&.MusecPpidVdevIino\&.host,S=\fIcnt\fR\(rq, or +\(lqtime\&.MusecPpidVdevIino_unique\&.host,S=\fIcnt\fR\(rq\&. +\(lqdev\(rq +is the message\*(Aqs device number, +\(lqino\(rq +is the message\*(Aqs inode number (from the previous +\fBfstat\fR(2) +call); and +\(lqcnt\(rq +is the message\*(Aqs size, in bytes\&. +.PP +The +\(lq,S=\fIcnt\fR\(rq +part optimizes the +\m[blue]\fBCourier\fR\m[]\&\s-2\u[3]\d\s+2 +mail server\*(Aqs maildir quota enhancement; it allows the size of all the mail stored in the maildir to be added up without issuing the +\fBstat\fR(2) +system call for each individual message (this can be quite a performance drain with certain network filesystems)\&. +.SS "READING MAIL FROM MAILDIRS" +.PP +Applications that read mail from maildirs should do it in the following order: +.PP +When opening a maildir or a maildir folder, read the +tmp +subdirectory and delete any files in there that are at least 36 hours old\&. +.PP +Look for new messages in the +new +subdirectory\&. Rename +\fInew/filename\fR, as +\fIcur/filename:2,info\fR\&. Here, +\fIinfo\fR +represents the state of the message, and it consists of zero or more boolean flags chosen from the following: +\(lqD\(rq +\- this is a \*(Aqdraft\*(Aq message, +\(lqR\(rq +\- this message has been replied to, +\(lqS\(rq +\- this message has been viewed (seen), +\(lqT\(rq +\- this message has been marked to be deleted (trashed), but is not yet removed (messages are removed from maildirs simply by deleting their file), +\(lqF\(rq +\- this message has been marked by the user, for some purpose\&. These flags must be stored in alphabetical order\&. New messages contain only the +:2, +suffix, with no flags, indicating that the messages were not seen, replied, marked, or deleted\&. +.PP +Maildirs may have maximum size quotas defined, but these quotas are purely voluntary\&. If you need to implement mandatory quotas, you should use any quota facilities provided by the underlying filesystem that is used to store the maildirs\&. The maildir quota enhancement is designed to be used in certain situations where filesystem\-based quotas cannot be used for some reason\&. The implementation is designed to avoid the use of any locking\&. As such, at certain times the calculated quota may be imprecise, and certain anomalous situations may result in the maildir actually going over the stated quota\&. One such situation would be when applications create messages without updating the quota estimate for the maildir\&. Eventually it will be precisely recalculated, but wherever possible new messages should be created in compliance with the voluntary quota protocol\&. +.PP +The voluntary quota protocol involves some additional procedures that must be followed when creating or deleting messages within a given maildir or its subfolders\&. The +\m[blue]\fB\fBdeliverquota\fR(8)\fR\m[]\&\s-2\u[4]\d\s+2 +command is a tiny application that delivers a single message to a maildir using the voluntary quota protocol, and hopefully it can be used as a measure of last resort\&. Alternatively, applications can use the +libmaildir\&.a +library to handle all the low\-level dirty details for them\&. The voluntary quota enhancement is described in the +\m[blue]\fB\fBmaildirquota\fR(7)\fR\m[]\&\s-2\u[5]\d\s+2 +man page\&. +.SS "Maildir Quotas" +.PP +This is a voluntary mechanism for enforcing "loose" quotas on the maximum sizes of maildirs\&. This mechanism is enforced in software, and not by the operating system\&. Therefore it is only effective as long as the maildirs themselves are not directly accessible by their users, since this mechanism is trivially disabled\&. +.PP +If possible, operating system\-enforced quotas are preferrable\&. Where operating system quota enforcement is not available, or not possible, this voluntary quota enforcement mechanism might be an acceptable compromise\&. Since it\*(Aqs enforced in software, all software that modifies or accesses the maildirs is required to voluntary obey and enforce a quota\&. The voluntary quota implementation is flexible enough to allow non quota\-aware applications to also access the maildirs, without any drastic consequences\&. There will be some non\-drastic consequences, though\&. Of course, non quota\-aware applications will not enforce any defined quotas\&. Furthermore, this voluntary maildir quota mechanism works by estimating the current size of the maildir, with periodic exact recalculation\&. Obviously non quota\-aware maildir applications will not update the maildir size estimation, so the estimate will be thrown off for some period of time, until the next recalculation\&. +.PP +This voluntary quota mechanism is designed to be a reasonable compromise between effectiveness, and performance\&. The entire purpose of using maildir\-based mail storage is to avoid any kind of locking, and to permit parallel access to mail by multiple applications\&. In order to compute the exact size of a maildir, the maildir must be locked somehow to prevent any modifications while its contents are added up\&. Obviously something like that defeats the original purpose of using maildirs, therefore the voluntary quota mechanism does not use locking, and that\*(Aqs why the current recorded maildir size is always considered to be an estimate\&. Regular size recalculations will compensate for any occasional race conditions that result in the estimate to be thrown off\&. +.PP +A quota for an existing maildir is installed by running maildirmake with the +\-q +option, and naming an existing maildir\&. The +\-q +option takes a parameter, +\fIquota\fR, which is a comma\-separated list of quota specifications\&. A quota specification consists of a number followed by either \*(AqS\*(Aq, indicating the maximum message size in bytes, or \*(AqC\*(Aq, maximum number of messages\&. For example: +.sp +.if n \{\ +.RS 4 +.\} +.nf +\fBmaildirmake \-q 5000000S,1000C \&./Maildir\fR +.fi +.if n \{\ +.RE +.\} +.PP +This sets the quota to 5,000,000 bytes or 1000 messages, whichever comes first\&. +.sp +.if n \{\ +.RS 4 +.\} +.nf +\fBmaildirmake \-q 1000000S \&./Maildir\fR +.fi +.if n \{\ +.RE +.\} +.PP +This sets the quota to 1,000,000 bytes, without limiting the number of messages\&. +.PP +A quota of an existing maildir can be changed by rerunning the +\fBmaildirmake\fR +command with a new +\-q +option\&. To delete a quota entirely, delete the +\fIMaildir\fR/maildirsize +file\&. +.SH "SEE ALSO" +.PP +\m[blue]\fB\fBmaildirmake\fR(1)\fR\m[]\&\s-2\u[1]\d\s+2\&. +.SH "AUTHOR" +.PP +\fBSam Varshavchik\fR +.RS 4 +Author +.RE +.SH "NOTES" +.IP " 1." 4 +\fBmaildirmake\fR(1) +.RS 4 +\%http://www.courier-mta.org/maildirmake.html +.RE +.IP " 2." 4 +RFC 1521 +.RS 4 +\%http://www.rfc-editor.org/rfc/rfc1521.txt +.RE +.IP " 3." 4 +Courier +.RS 4 +\%http://www.courier-mta.org +.RE +.IP " 4." 4 +\fBdeliverquota\fR(8) +.RS 4 +\%http://www.courier-mta.org/deliverquota.html +.RE +.IP " 5." 4 +\fBmaildirquota\fR(7) +.RS 4 +\%http://www.courier-mta.org/maildirquota.html +.RE |