Quota Plugin

Quota tracking and enforcing plugin.

Three plugins are associated with quota:

Name

Description

imap_quota

Enables IMAP commands for requesting and adminstering current quota.

quota

Implements the actual quota handling and includes all quota backends.

quota_clone

Copy the current quota usage to a dict.

Quota backend specifies the method how Dovecot keeps track of the current quota usage. They don’t (usually) specify users’ quota limits, that’s done by returning extra fields from userdb. There are different quota backends that Dovecot can use:

Backend

Description

count

Store quota usage within Dovecot’s index files.

New in version v2.2.19.

dict

Store quota usage in a dictionary (e.g. SQL, or flat files).

dirsize

The simplest and slowest quota backend.

fs

Filesystem quota.

imapc

Use quota from remote IMAP server with imapc.

New in version v2.2.30.

maildir

Store quota usage in Maildir++ maildirsize files. This is the most commonly used quota for virtual users.

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.)

Quota Service

The quota service allows postfix to check quota before delivery:

service quota-status {
  executable = quota-status -p postfix
  inet_listener {
    port = 12340
    # You can choose any port you want
  }
  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://blog.sys4.de/postfix-dovecot-mailbox-quota-en.html

Enabling Quota Plugins

Enable in configuration files, e.g.:

conf.d/10-mail.conf:

# Enable quota plugin for tracking and enforcing the quota.
mail_plugins = $mail_plugins quota

conf.d/20-imap.conf:

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

conf.d/90-quota.conf: (for use with the quota-status service)

plugin {
  quota_grace = 10%%
  # 10% is the default
  quota_status_success = DUNNO
  quota_status_nouser = DUNNO
  quota_status_overquota = "552 5.2.2 Mailbox is full"
}

Configuration

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 autoexpunge <namespaces_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

Example

To use the recommended count quota driver:

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

plugin {
  quota = count:User quota
  quota_max_mail_size = 100M
  # Required for 'count' quota driver
  quota_vsizes = yes

Associated Plugins

Quota Drivers