maildirquota(7) - man - phpMan

MAILDIRQUOTA(7)                        Double Precision, Inc.                        MAILDIRQUOTA(7)



NAME
       maildirquota - voluntary Maildir quotas

SYNOPSIS
       maildirmake {-q} {10000000S} {./Maildir}

DESCRIPTION
       maildrop has a manual quota enforcement implementation that does use the quota facilities of
       the host operating system (filesystem-based quotas). This is an option that is set at
       configuration time, and may be disabled.

       Using filesystem quotas sometimes leads to problems. After a hard quota is hit, most commands
       issued by mail clients fail, including some commands that poorly-written mail software may
       not expect to fail, and therefore be unable to gracefully handle the unexpected failure.

       With manual quotas, the only operations that fail are the ones that most mail clients expect
       to fail, when the mailbox is full. However, filesystem-based quotas cannot be used in some
       situations, such as virtual mailboxes. If this experimental feature is enabled, approximate
       quota enforcement can be implemented by maildrop or deliverquota to whatever extent it's
       possible to do so. Quotas are enabled by the -q option to maildirmake. Both maildrop and
       deliverquota will observe any maildirmake-requested quota.

   LIMITATIONS
       This quota mechanism will only work as long as maildrop (or deliverquota) are the only
       applications that deliver messages to the maildir, or as long as other applications implement
       the same quota enforcement mechanism. The quota enforcement mechanism is described separately
       in the README.maildirquota.html file in the source code distribution.

       Quota enforcement will still work, to some extent, if there are other applications that
       deliver or modify messages in the maildir. However, quota enforcement may not kick in
       immediately when the maildir goes over quota, in fact the maildir can go over quota by a
       noticeable amount. But eventually, as long as maildrop or deliverquota are responsible for
       delivering the majority of messages, quota enforcement will kick in. Also, other sources of
       messages may also result in noticeable performance degradation, because quote recalculation
       will become noticeably more expensive.

       Also keep in mind that this quota mechanism is generally useless if mail recipients have
       direct access to their maildirs.

       Finally even under the best conditions this quota enforcement does have a small chance of a
       race condition where a maildir will go over quota by some amount. maildirs are designed for
       speed, and this quota implementation was designed to have as little additional overhead as
       possible, compared to regular maildirs. To enforce an exact quota you would have to use some
       kind of a locking facility, which will impose a drastic performance degradation on the
       overall maildir performance. A decision has been made to avoid locking, with the only
       negative side effect being a possibility of going over quota in very low probability
       situations.

       A way to minimize the risk of going over quota is to set reasonable quotas, in relation to
       maximum message sizes supported by your mail server. If you set your maildir quota to five
       gigabytes, for example, it makes very little sense to configure your mail server to accept
       messages up to three gigabytes in size. Your maildir quota should be chosen so that it makes
       sense when compared to the maximum message size allowed by your mail server.

   FOLDERS
       This quota implementation is compatible with a popular extension to maildir which defines
       individual mail folders within a single maildir. However, in order to create a compatible
       folder, you MUST use the maildirmake command that comes with maildrop, and you MUST use the
       -f option to maildirmake, giving the name of the folder. Do not use maildirmake and specify
       the directory name of the maildir folder. Quota enforcement will not work if you do that.

SEE ALSO
       maildrop(1)[1], maildirmake(1)[2], maildropfilter(5)[3], deliverquota(8)[4].

AUTHOR
       Sam Varshavchik
           Author

NOTES
        1. maildrop(1)
           http://www.courier-mta.org/maildrop.html

        2. maildirmake(1)
           http://www.courier-mta.org/maildirmake.html

        3. maildropfilter(5)
           http://www.courier-mta.org/maildropfilter.html

        4. deliverquota(8)
           http://www.courier-mta.org/deliverquota.html



Courier Mail Server                          07/24/2017                              MAILDIRQUOTA(7)