Provided by: courier-base_0.47-13ubuntu5_i386 bug


       maildirquota - voluntary Maildir quotas


       maildirmake -q 10000000S ./Maildir


       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
       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.

       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

       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

       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
       messages  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.

       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.


       maildrop(1), maildirmake(1), maildropfilter(5), deliverquota(8).