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Quota Plugin (quota) ​

Quota tracking and enforcing plugin.

Three plugins are associated with quota:

NameDescription
imap-quota pluginEnables IMAP commands for requesting and administering current quota.
quota (this plugin)Implements the actual quota handling and includes all quota drivers.
quota-clone pluginCopy the current quota usage to a dict.

Configuration ​

Enabling Quota Plugins ​

Enable in configuration files, e.g.:

# Enable quota plugin for tracking and enforcing the quota.
mail_plugins {
  quota = yes
}

protocol imap {
  # Enable the IMAP QUOTA extension, allowing IMAP clients to ask for the
  # current quota usage.
  mail_plugins {
    imap_quota = yes
  }
}

# Keep this setting outside the quota { .. } to allow easily overriding it
# in userdb lookups.
quota_storage_size = 1G

quota "User quota" {
}

Quota Root ​

Quota root is a concept from IMAP Quota specifications (RFC 2087). Normally you'll have only one quota root, but in theory there could be, e.g., "user quota" and "domain quota" roots. It's unspecified how the quota roots interact with each other (if at all).

In some systems, for example, INBOX could have a completely different quota root from the rest of the mailboxes (e.g. INBOX in /var/mail/ partition and others in /home/ partition).

Quota Limits ​

There are two types of quota limits:

  • Message count limits
  • Storage size limits

The message count limit is calculated as: quota_message_count * quota_message_percentage. Zero is assumed to be unlimited.

The storage size limit is calculated as: quota_storage_size * quota_storage_percentage + quota_storage_extra. Zero is assumed to be unlimited.

The percentage and extra values are mainly useful to allow exceeding the regular quota limit in some mailboxes, such as allowing clients that move messages with IMAP COPY+EXPUNGE to Trash folder to temporarily exceed the quota.

Example ​

quota_storage_size = 1G
namespace inbox {
  mailbox Trash {
    quota_storage_extra = 100M
  }
  mailbox SPAM {
    quota_ignore = yes
  }
}

This means that the user has 1GB quota, but when saving messages to Trash mailbox it's possible to use up to 1.1GB of quota. The quota isn't specifically assigned to Trash, so if you had 1GB of mails in Trash you could still save 100MB of mails to Trash, but nothing to other mailboxes.

Additionally, any messages in the SPAM folder are ignored and would not count against the quota at all.

Per-User Quota ​

You can override the quota settings in your userdb: Extra Fields. Keep global settings in configuration plugin section and override only those settings you need to in your userdb.

Use doveadm user command to verify that the userdb returns the expected quota settings.

Override: LDAP ​

Example LDAP authentication where the quota limit is in quotaBytes field:

userdb ldap {
  ...
  fields {
    home = %{ldap:homeDirectory}
    quota_storage_size = {ldap:quotaBytes}B
  }
}

Override: SQL ​

Example (for MySQL):

userdb sql {
  query = SELECT uid, gid, home, CONCAT(quota_limit_bytes, 'B') AS quota_storage_size \
    FROM users \
    WHERE userid = '%{user}'

passdb sql {
  # SQL with userdb prefetch: Remember to prefix quota_quota_storage_size with userdb_
  # (just like all other userdb extra fields):
  query = SELECT userid AS user, password, uid AS userdb_uid, gid AS userdb_gid, \
      CONCAT(quota_limit_bytes, 'B') AS userdb_quota_storage_size \
    FROM users \
    WHERE userid = '%{user}'
}

Example (for PostgreSQL and SQLite):

sql_driver = sqlite # alternatively: pgsql

userdb sql {
  query = SELECT uid, gid, home, quota_limit_bytes || 'B' AS quota_storage_size \
    FROM users \
    WHERE userid = '%{user}'
}

Override: passwd-file ​

Example passwd-file authentication database entries:

user:{plain}pass:1000:1000::/home/user::userdb_quota_storage_size=100M
user2:{plain}pass2:1001:1001::/home/user2::userdb_quota_storage_size=200M
user3:{plain}pass3:1002:1002::/home/user3::userdb_mail_path=~/Maildir userdb_quota_storage_size=300M

Override: passwd ​

The passwd authentication database userdb doesn't support extra fields. That's why you can't directly set users' quota limits to passwd file. You can use an additional userdb (e.g. passwd-file authentication database where only the quota limits are specified.

Quota for Public Namespaces ​

You can create a separate namespace-specific quota that's shared between all users. This is done by configuring the quota root inside the namespace filter. For example:

namespace public {
  type = public
  prefix = Public/
  #mail_path = ..

  quota "Shared quota" {
    #quota_storage_size = ...
  }
}

quota "User quota" {
  #quota_storage_size = ...
}

Note that globally configured quota roots are used only for private namespaces.

Quota for Private Namespaces ​

You can create a separate namespace-specific quota for a folder hierarchy. This is done by configuring the quota root inside the namespace filter. For example:

namespace inbox {
  quota "User quota" {
    #quota_storage_size = ...
  }
}

namespace archive {
  type = private
  prefix = Archive/
  #mail_path = ..

  quota "Archive quota" {
    #quota_storage_size = ...
  }
}

Note that both quotas must be configured inside the namespace filter. Using a global quota configuration would apply to both namespaces.

Quota and Shared Namespaces ​

Quota plugin considers shared namespaces against owner's quota, not the current user's. The regular private quota configuration is used - there is no need to explicitly configure quota for shared namespaces. The quota limits are also taken from the userdb.

Public namespaces are ignored unless there is explicit quota specified for it.

Custom Quota Exceeded Message ​

See quota_exceeded_message.

Example:

quota_exceeded_message = Quota exceeded, please go to http://www.example.com/over_quota_help for instructions on how to fix this.

Quota Drivers ​

Quota driver specifies the method how Dovecot keeps track of the current quota usage. They don't specify users' quota limits - that's done by returning extra fields from userdb.

We recommend using count for any new installations.

If you need usage data to an external database, consider using quota-clone plugin for exporting the information. (It's very slow to query every user's quota from the index files directly.)

Driver: Count ​

The count quota driver tracks the quota internally within Dovecot's index files.

INFO

This is the RECOMMENDED way of calculating quota on recent Dovecot installations.

Each mailbox's quota is tracked separately and when the current quota usage is wanted to be known, the mailboxes' quotas are summed up together. To get the best performance, make sure mailbox_list_index = yes.

WARNING

If you're switching from some other quota driver to count, make sure that all the mails have their virtual sizes already indexed. Otherwise there may be a significant performance hit when Dovecot starts opening all the mails to get their sizes. You can help to avoid this by accessing the mailbox vsizes for all the users before doing the configuration change: doveadm mailbox status -u user@domain vsize '\*'.

Configuration ​

count driver doesn't have any additional parameters.

mailbox_list_index = yes

# Avoid spending excessive time waiting for the quota calculation to finish
# when mails' vsizes aren't already cached. If this many mails are opened,
# finish the quota calculation on background in indexer-worker process. Mail
# deliveries will be assumed to succeed, and explicit quota lookups will
# return internal error.
protocol !indexer-worker {
  mail_vsize_bg_after_count = 100
}

# 10MB quota limit
quota_storage_size = 10M

quota "User quota" {
}

Driver: fs ​

The fs (filesystem) quota driver supports both local filesystems and rquota (NFS).

Configuration ​

quota_fs_message_limit
Defaultno
Valueboolean

If yes, use filesystem quota's inode limit as the message count limit. This can be useful with Maildir or sdbox. Used only with Quota Driver: Filesystem.

quota_fs_mount_path
Default[None]
Valuestring

If specified, enable FS quota for the specified mount path. Only mailboxes existing in this mount path have the quota enabled. Empty value looks up the mountpoint automatically. Used only with Quota Driver: Filesystem.

quota_fs_type
Defaultany
Valuestring
Allowed Valuesanyusergroup

Using any attempts to use the user quota first, with a fallback to group quota. Using user or group only attempts to use the user or the group quota, with a fallback to unlimited quota limit. Used only with Quota Driver: Filesystem.

Systemd ​

If you are using systemd, please make sure you turn offPrivateDevices=yes, otherwise the driver won't work properly. The best way to do this is to use systemctl edit dovecot command or add file /etc/systemd/system/dovecot.service.d/override.conf with:

[Service]
PrivateDevices=off

Index Files ​

It's a good idea to keep index files in a partition where there are no filesystem quota limits. The index files exist to speed up mailbox operations, so Dovecot runs more slowly if it can't keep them updated. You can specify the index file location with the mail_index_path setting.

Dovecot can handle "out of disk space" errors in index file handling and transparently move to in-memory indexes. It'll use the in-memory indexes until the mailbox is re-opened.

mbox ​

It's a good idea to have mbox_lazy_writes = yes (default), otherwise Dovecot might give "Not enough disk space" errors when opening the mailbox, making it impossible to expunge any mails.

If user has run out of quota and index files are also in memory (because they're also over quota), it's possible that message flag changes are lost. This should be pretty rare though because Dovecot keeps some extra space allocated inside the mbox file for flag changes.

Example:

mail_driver = mbox
mail_path = ~/mail
mail_inbox_path = /var/mail/%{user}
mail_index_path = /var/no-quotas/index/%{user}

Maildir ​

Maildir needs to be able to add UIDs of new messages to dovecot-uidlist file. If it can't do this, it can give an error when opening the mailbox, making it impossible to expunge any mails.

Currently the only way to avoid this is to use a separate partition for the uidlist files where there are no filesystem quota limits. You can do this with the mail_control_path setting.

Example:

mail_driver = maildir
mail_path = ~/Maildir
mail_index_path = /var/no-quotas/index/%{user}
mail_control_path = /var/no-quotas/control/%{user}

Note that if you change the location of the control files, Dovecot will look in the new control path directory (/var/no-quotas/control/%{user}) for the mailbox subscriptions file.

Configuration Examples ​

mail_plugins {
  quota = yes
}
protocol imap {
  mail_plugins {
    imap_quota = yes
  }
}

quota user {
  driver = fs
}

If you want to see both user and group quotas as separate quota roots, you can use:

quota "User quota" {
  driver = fs
  fs_type = user
}
quota "Group quota" {
  driver = fs
  fs_type = group
}

If you have your mails in two filesystems, you can create two quota roots:

quota INBOX {
  driver = fs
  # Assuming INBOX in /var/mail/ which is mounted to /
  fs_mount_path = /
}
quota Others {
  driver = fs
  # Assuming other mailboxes are in /home mount
  fs_mount_path = /home
}

Driver: imapc ​

See Imapc: Quota.

Configuration ​

Driver: maildir ​

WARNING

Note that Maildir++ quota works only with Maildir format. However, even with Maildir format the recommendation is to use count.

The maildir quota driver implements Maildir++ quota in Dovecot. Dovecot implements the Maildir++ specification so Dovecot remains compatible with Courier, maildrop, Exim, etc.

Maildirsize File ​

The maildirsize file in the Maildir root directory contains both the quota limit information and the current quota status. It contains a header in format:

<storage limit in bytes>S,<messages limit>C

Removed: 2.4.0 Maildir++ quota limit must now be specified in Dovecot configuration. It will no longer be read from the maildirsize file. The limits are still written to the file header, but they are ignored by Dovecot.

Maildir++ quota relies on maildirsize file having correct information, so if your users can modify the file in some way (e.g. shell access), you're relying on the goodwill of your users for the quota to work.

You can't rely on Dovecot noticing external changes to Maildir and updating maildirsize accordingly. This happens eventually when quota is being recalculated, but it may take a while. Quota recalculation also won't trigger quota warning executions.

Once the maildirsize reaches 5120 bytes, the quota is recalculated and the file is recreated. This makes sure that if quota happens to be broken (e.g. externally deleted files) it won't stay that way forever.

Quota Service ​

The quota service allows Postfix to check quota before delivery. This service does not support proxying, so it works only in non-clustered setups when there is a single Dovecot server.

service quota-status {
  executable = quota-status -p postfix
  inet_listener {
    # You can choose any port you want
    port = 12340
  }
  client_limit = 1
}

And then have postfix check_policy_service check that:

smtpd_recipient_restrictions =
  ...
  check_policy_service inet:mailstore.example.com:12340

For more about this service, see https://sys4.de/en/blog/postfix-dovecot-mailbox-quota/

Quota Warning Scripts ​

You can configure Dovecot to run an external command when user's quota exceeds a specified limit. Note that the warning is ONLY executed at the exact time when the limit is being crossed, so when you're testing you have to do it by crossing the limit by saving a new mail. If something else besides Dovecot updates quota so that the limit is crossed, the warning is never executed.

The quota warning limits are configured the same way as the actual Quota Limits, but just placed inside the quota_warning filter.

Only the command for the first exceeded limit is executed, so configure the highest limit first. The actual commands that are run need to be created as services (create a named Dovecot service and use the service name as the `quota-warning socket name` argument).

Configuration ​

quota_warning

Default[None]
ValueNamed List Filter
See Also

Create a new quota warning. The filter name refers to quota_warning_name setting. The execute setting is required to be specified inside the filter.

The order of quota_warning filters in the configuration is important: Only the first warning that matches the rules is executed. This means you must configure the highest limits first.

quota_warning_threshold

Defaultover
Valuestring
Allowed Valuesoverunder
See Also

Should the quota warning be executed when quota grows over the limit, or when it drops under the limit.

Example Configuration ​

quota user {
  warning warn-95 {
    quota_storage_percentage = 95
    execute quota-warning {
      args = 95 %{user}
    }
  }
  warning warn-80 {
    quota_storage_percentage = 80
    execute quota-warning {
      args = 80 %{user}
    }
  }
  warning warn-under {
    quota_storage_percentage = 100
    # user is no longer over quota
    threshold = under
    execute quota-warning {
      args = below %{user}
    }
  }
}

service quota-warning {
  executable = script /usr/local/bin/quota-warning.sh
  # use some unprivileged user for executing the quota warnings
  user = vmail
  unix_listener quota-warning {
  }
}

With the above example, when user's quota exceeds 80% quota-warning.sh is executed with parameter 80. The same goes for when quota exceeds 95%. If user suddenly receives a huge mail and the quota jumps from 70% to 99%, only the 95 script is executed.

You have to create the quota-warning.sh script yourself. Here is an example that sends a mail to the user:

Example quota-warning.sh
sh
#!/bin/sh
PERCENT=$1
USER=$2
cat << EOF | /usr/local/libexec/dovecot/dovecot-lda -d $USER -o quota_enforce=no
From: postmaster@domain.com
Subject: quota warning

Your mailbox is now $PERCENT% full.
EOF

The quota enforcing is disabled to avoid looping.

Overquota-flag ​

Quota warning scripts can be used to set an overquota-flag to userdb (e.g. LDAP) when user goes over/under quota. This flag can be used by MTA to reject mails to an user who is over quota already at SMTP RCPT TO stage.

A problem with this approach is there are race conditions that in some rare situations cause the overquota-flag to be set even when user is already under quota. This situation doesn't solve itself without manual admin intervention or the overquota-flag feature: This feature checks the flag's value every time user logs in (or when mail gets delivered or any other email access to user) and compares it to the current actual quota usage. If the flag is wrong, a script is executed that fixes up the situation.

The execute setting inside quota_over_status named filter specifies the script that is executed. The current quota_over_status_current value is appended as the last parameter.

The overquota-flag name in userdb must be quota_over_status_current.

These settings are available:

Example:

quota_over_status {
  # If quota_over_status_current=TRUE, the overquota-flag is enabled.
  # Otherwise not.
  mask = TRUE

  # Any non-empty value for quota_over_status_current means user is over quota.
  # Wildcards can be used in a generic way, e.g. "*yes" or "*TRUE*"
  #mask = *

  lazy_check = yes
  execute quota-warning {
    args = mismatch %{user}
  }
}

Quota Grace ​

See quota_storage_grace.

By default the last mail can bring user over quota. This is useful to allow user to actually unambiguously become over quota instead of fail some of the last larger mails and pass through some smaller mails. Of course the last mail shouldn't be allowed to bring the user hugely over quota, so by default this limit is 10 MB.

To change the quota grace, use:

# allow user to become max 50 MB over quota
quota_storage_grace = 50 M
}

Maximum Mailbox Count ​

See quota_mailbox_count.

Maximum number of mailboxes that can be created. Each namespace is tracked separately, so e.g. shared mailboxes aren't counted towards the user's own limit. The default is 0, which is unlimited.

Maximum Messages Per Mailbox ​

See quota_mailbox_message_count.

Maximum number of messages that can be created in a single mailbox.

Maximum Saved Mail Size ​

See quota_mail_size.

Dovecot allows specifying the maximum message size that is allowed to be saved (e.g. by LMTP, IMAP APPEND or doveadm save). The default is unlimited.

Since outgoing mail sizes are also typically limited on the MTA side, it can be beneficial to prevent user from saving too large mails, which would later on fail on the MTA side anyway.

Quota Virtual Sizes ​

Indicates that the quota plugin should use virtual sizes rather than physical sizes when calculating message sizes. Required for the count driver.

This is automatically determined by the quota plugin.

Quota Admin Commands ​

The imap-quota plugin implements the SETQUOTA command, which allows changing the logged in user's quota limit if the user is admin.

See imap-quota plugin for further configuration information.

Quota Recalculation ​

If your quotas are out of sync, you can use doveadm quota recalc -u <uid> command to recalculate them.

Quota and Trash Mailbox ​

Standard way to expunge messages with IMAP works by:

  1. Marking message with \Deleted flag
  2. Actually expunging the message using EXPUNGE command

Both of these commands can be successfully used while user's quota is full. However many clients use a move-to-Trash feature, which works by:

  1. COPY the message to Trash mailbox
  2. Mark the message with \Deleted
  3. Expunge the message from the original mailbox
  4. (Maybe later expunge the message from Trash when clean trash feature is used)

If user is over quota (or just under it), the first COPY command will fail and user may get an unintuitive message about not being able to delete messages because user is over quota. The possible solutions for this are:

  • Disable move-to-trash feature from client
  • You can create a separate quota rule ignoring Trash mailbox's quota. Note that this would allow users to store messages infinitely to the mailbox.
  • You can create a separate quota rule giving Trash mailbox somewhat higher quota limit (but not unlimited).

To make sure users don't start keeping messages permanently in Trash you can use mailbox_autoexpunge to expunge old messages from Trash mailbox.

Debugging Quota ​

User's current quota usage can be looked up with doveadm quota get -u user@domain.

User's current quota may sometimes be wrong for various reasons (typically only after some other problems). The quota can be recalculated with doveadm quota recalc -u user@domain.

Quota Status Service ​

Dovecot supports quota-status service, which uses Postfix-compatible policy server protocol. This allows Postfix to check the quota before mail delivery.

Example:

service quota-status {
  executable = quota-status -p postfix
  unix_listener /var/spool/postfix/private/quota-status {
    user = postfix
  }
  # Or with TCP:
  inet_listener postfix {
    # You can choose any port you want
    port = 12340
  }
  client_limit = 1
}
smtpd_recipient_restrictions =
  ...
  check_policy_service unix:private/quota-status
  # Or with TCP:
  #check_policy_service inet:mailstore.example.com:12340

Configuration ​

Settings ​

quota

Default[None]
ValueNamed List Filter
See Also

Create a new quota root. The filter name refers to quota_name setting.

Globally configured quota roots are used only for private namespaces. To use quota for public namespaces, configure it inside the public namespace.

Example:

quota "User quota" {
  storage_size = 1G
}

quota_enforce

Defaultyes
quota_imapc { no }
Valueboolean

If disabled, the quota limit isn't actually enforced. The quota is still tracked and the current quota usage is visible to IMAP GETQUOTA commands.

quota_exceeded_message

DefaultQuota exceeded (mailbox for user is full)
Valuestring

The message specified here is passed on to a user who goes over quota. There are also other messages, which are currently hard coded:

quota_fs_message_limit

Defaultno
Valueboolean

If yes, use filesystem quota's inode limit as the message count limit. This can be useful with Maildir or sdbox. Used only with Quota Driver: Filesystem.

quota_fs_mount_path

Default[None]
Valuestring

If specified, enable FS quota for the specified mount path. Only mailboxes existing in this mount path have the quota enabled. Empty value looks up the mountpoint automatically. Used only with Quota Driver: Filesystem.

quota_fs_type

Defaultany
Valuestring
Allowed Valuesanyusergroup

Using any attempts to use the user quota first, with a fallback to group quota. Using user or group only attempts to use the user or the group quota, with a fallback to unlimited quota limit. Used only with Quota Driver: Filesystem.

quota_hidden

Defaultno
Valueboolean

If yes, hide the quota root from IMAP GETQUOTA commands.

quota_ignore

Defaultno
Valueboolean

If yes, don't include this mailbox or namespace in quota calculations.

Example:

namespace inbox {
  mailbox Trash {
    quota_ignore = yes
  }
}
namespace secondary {
  quota_ignore = yes
}

quota_ignore_unlimited

Defaultno
Valueboolean

If yes, ignore the quota root entirely if it has no quota limits. This means no tracking of the quota, and not making it visible to IMAP GETQUOTA commands.

quota_mailbox_count

Defaultunlimited
Valueunsigned integer
See Also
Changes
  • Added: 2.4.0

Maximum number of mailboxes that can be created. Each namespace is tracked separately, so e.g. shared mailboxes aren't counted towards the user's own limit.

quota_mailbox_message_count

Defaultunlimited
Valueunsigned integer
Changes
  • Added: 2.4.0

Maximum number of messages that can be created in a single mailbox.

quota_message_percentage

Default100
Valueunsigned integer
See Also

Multiplier for the quota_message_count setting (in this mailbox/namespace).

This may be useful to exceed the regular quota limit in some mailboxes, such as allowing clients that move messages with IMAP COPY+EXPUNGE to Trash folder to temporarily exceed the quota.

Example:

quota_message_count = 10000
namespace inbox {
  mailbox Trash {
    # 110% * 10000 = 11000 limit
    quota_message_percentage = 110
  }
}

quota_name

Default[None]
Valuestring
See Also

Name of the quota root. The quota filter name refers to this setting.

The quota root name is just an arbitrary string that is sent to IMAP clients, which in turn may show it to the user. The name has no meaning.

quota_over_status_current

Default[None]
Valuestring
See Also

An identifier that indicates whether the overquota-flag is active for a user.

This identifier is compared against quota_over_status_mask to determine if the overquota-flag should be set for the user.

Usually, this value will be loaded via userdb.

quota_over_status_lazy_check

Defaultno
Valueboolean

If enabled, overquota-flag is checked only when current quota usage is going to already be checked anyway. This prevents any additional storage I/O that would be caused by the overquota-flag check.

quota_storage_extra

Default0
Valuesize
See Also

If set, increase the quota_storage_size (for the mailbox/namespace) by this amount. This is an alternative to using quota_storage_percentage, although both can also be used.

This may be useful to exceed the regular quota limit in some mailboxes, such as allowing clients that move messages with IMAP COPY+EXPUNGE to Trash folder to temporarily exceed the quota.

Example:

quota_storage_size = 1G
namespace inbox {
  mailbox Trash {
    # 1G + 100M = 1100M
    quota_storage_extra = 100M
  }
}

quota_storage_grace

Default10 M
Valuesize
See Also

If set, allows message deliveries (LDA, LMTP) to exceed quota once by this amount. After the quota is already over the limit, the grace no longer applies. This prevents a situation where some smaller mails may still become delivered, but larger mail deliveries fail, and the user may not have received any warning about reaching the quota limit.

quota_storage_percentage

Default100
Valueunsigned integer
See Also

Multiplier for the quota_storage_size setting (in this mailbox/namespace). This is an alternative to using quota_storage_extra, although both can also be used.

This may be useful to exceed the regular quota limit in some mailboxes, such as allowing clients that move messages with IMAP COPY+EXPUNGE to Trash folder to temporarily exceed the quota.

Example:

quota_storage_size = 1G
namespace inbox {
  mailbox Trash {
    # 110% * 1G = 1100M
    quota_storage_percentage = 110
  }
}

quota_warning

Default[None]
ValueNamed List Filter
See Also

Create a new quota warning. The filter name refers to quota_warning_name setting. The execute setting is required to be specified inside the filter.

The order of quota_warning filters in the configuration is important: Only the first warning that matches the rules is executed. This means you must configure the highest limits first.

quota_warning_threshold

Defaultover
Valuestring
Allowed Valuesoverunder
See Also

Should the quota warning be executed when quota grows over the limit, or when it drops under the limit.

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