MAILDIRQUOTA(7)MAILDIRQUOTA(7)NAMEmaildirquota - voluntary Maildir quotas
SYNOPSIS
maildirmake -q 10000000S ./Maildir
DESCRIPTION
maildrop has an experimental quota enforcement implementation. This is
an option that is set at configuration time, and may be disabled.
Filesystem-based quotas should be used whenever possible. However
filesystem-based quotas cannot be used in some situations, such as vir‐
tual 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 deliv‐
erquota) 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 dis‐
tribution.
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 imple‐
mentation was designed to have as little additional overhead as possi‐
ble, compared to regular maildirs. To enforce an exact quota you would
have to use some kind of a locking facility, which will impose a dras‐
tic 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 megabytes, for example,
it makes very little sense to configure your mail server to accept mes‐
sages up to three megabytes long. 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 ALSOmaildrop(1), maildirmake(1), maildropfilter(5), deliverquota(8).
Double Precision, Inc. 19 February 2004 MAILDIRQUOTA(7)
