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# Quotas

Optional feature

This feature is completely optional. If you are eager to get finished then skip this page and maybe come back later.

Potential breakage with virtual_aliases

Do not use the `check_policy_service` if you are using virtual_aliases. See Julien’s comment. We need to find a solution for that.

Quotas are size limits for users. You can make sure that users do not waste arbitrary amounts of disk space but are forced to clean up old emails every now and then.

The magic happens in two places:

1. Dovecot needs to keep track of the quota and how much the user has already used up of it.
2. Postfix needs to reject new emails if the user’s mailbox is over quota.

## Dovecot

Section titled “Dovecot”

### Enable quota service

Section titled “Enable quota service”

As usual we need a new piece of configuration to enable the quota plugin and define how we want it to behave:

Run this on your server

    cat > /etc/dovecot/conf.d/99-ispmail-quota.conf << 'EOF'# Enable the quota pluginmail_plugins {  quota = yes}
    # Set global defaults. Keep this outside of a "quota {}" section so that it# can be overriden with data from the virtual_users table.# Allow 5 GB of space per default.quota_storage_size = 5G
    # It is important to allow it so that Postfix can deliver an email to# bring the user above 100% of quota usage. Otherwise you risk that the user# is at 99.99% of quota but the last email cannot be delivered and gets stuck# between Postfix and Dovecot. No email should be larger than this.quota_storage_grace = 50M
    # Define two warnings at 80% and 95% of quota usage.quota "User quota" {  # Set one warning level to 100%  warning warn-100 {    quota_storage_percentage = 100    execute quota-warning {      args = 100 %{user}    }  }
      # Set another warning level to 80% for early warnings  warning warn-80 {    quota_storage_percentage = 80    execute quota-warning {      args = 80 %{user}    }  }
      # User is no longer over quota  warning warn-under {    quota_storage_percentage = 100    threshold = under    execute quota-warning {      args = below %{user}    }  }}
    # Define what happens if the user goes over quota. Point to a script that# creates a warning email to the user. The name "quota-warning" corresponds# to the "execute" statement in the warning definitions.service quota-warning {  executable = script /usr/local/bin/ispmail-quota-warning.sh  unix_listener quota-warning {    mode = 0660    user = vmail    group = vmail  }}
    # Add a new service so that Postfix can check if a user is over quota.# It listens on TCP port 13373.service quota-status {  executable = quota-status -p postfix  inet_listener quota-status {    listen = 127.0.0.1    port = 13373  }  client_limit = 1}
    # Enable the IMAP QUOTA extension, allowing IMAP clients to ask for the# current quota usage. Roundcube displays the current space usage in# the lower left corner.protocol imap {  mail_plugins {    imap_quota = yes  }}EOF
    # Apply the configurationsystemctl reload dovecot

The script that is launched by the `quota-warning` service is pretty simple. It sends an email to the affected user. It uses the special way of `dovecot-lda -o quota_enforce=no` though so that the warning email itself is always delivered even if the user is over quota.

Run this on your server

    cat > /usr/local/bin/ispmail-quota-warning.sh << 'EOF'#!/bin/bash## This script is part of the ISPmail configuration.# It is called from /etc/dovecot/conf.d/99-ispmail-quota.conf# and sends an email to the user if the quota is at 80%, over 100%# or back below 100%.## Christoph Haas <ispmail@christoph-haas.de># Version 1.0 – 2025-12-30
    LEVEL=$1USER=$2MAIL="From: postmaster@${USER#*@}"MAIL+="\nSubject: Quota information"MAIL+="\nX-Priority: 1"MAIL+="\n\nThis is an automatic email from your friendly mail server.\n\n"
    if [ $LEVEL = "below" ]; then  MAIL+="Thanks for making some space. You will now be able to receive emails again."elif [ $LEVEL -eq 80 ]; then  MAIL+="Your mailbox is currently using up 80% of the maximum space."  MAIL+="\nPlease consider deleting some emails. If your used space reached"  MAIL+="\n100% then you would not be able to receive further emails. I will"  MAIL+="\nhowever send you another email in that case."  MAIL+="\n"  MAIL+="\nThanks for your attention."elif [ $LEVEL -eq 100 ]; then  MAIL+="I am afraid to tell you that your mailbox is now 100% full."  MAIL+="\nNew emails to your address will be rejected by the server."  MAIL+="\nPlease delete some emails immediately. I will send you another"  MAIL+="\nemail once you have made some space."  MAIL+="\n"  MAIL+="\nThanks for your attention."fi
    echo -e $MAIL | /usr/lib/dovecot/dovecot-lda -d $USER -o quota_enforce=noEOF
    chmod u=rwx,g=rx,o= /usr/local/bin/ispmail-quota-warning.shchown vmail:vmail /usr/local/bin/ispmail-quota-warning.sh

### Global versus local

Section titled “Global versus local”

By default you will probably allow all users to use a certain amount of disk space for their emails. That would be the global value that you set using `quota_storage_size = …`.

But maybe you have some special users that need a different value. For a power user you could allow more space than for other users. Then set the `quota` field in his record in the `virtual_users` table to a value larger than 0.

So the logic for the `quota` field in the database is:

- 0 means: take the global setting of `quota_storage_size`
- anything else: override by this value (in bytes)

We added that logic into the `userdb sql` section earlier:

    IF(quota > 0, CONCAT(quota, 'B'), NULL) AS quota_storage_size

That’s the SQL way of saying: if “quota” is 0, then return NULL. NULL tells Dovecot to fall back to the global value. Otherwise add a “B” (for “bytes” – Dovecot requires that) and return that.

### Showing current usage

Section titled “Showing current usage”

Now that quota restrictions are in place, you can ask Dovecot for the current status of all mailboxes:

Run this on your server

    doveadm quota get -A

You will get output like this:

    Username         Quota name Type       Value     Limit  %john@example.org User quota STORAGE    22856   1048576  2john@example.org User quota MESSAGE       19         -  0

John is shown twice because Dovecot keeps track of:

- the amount of storage John uses (`STORAGE`)
- the number of emails that John has (`MESSAGE`)

The current configuration just cares about the space that is used on disk. So in the above example he has 22,856 KB used of the 1 GB limit – which is 2%. And he has a total of 19 messages but there is no limit to that.

### Testing the quota service (optional)

Section titled “Testing the quota service (optional)”

You may wonder why there is a `quota-status` service. If a user is over quota then it would reject an more incoming emails. But Postfix – which sits in front front of Dovecot – would still happily accept more emails. For a sender on a remote server it looks like the email was delivered. But it’s now stuck between Postfix and Dovecot until the user makes some space.

The obvious solution: Postfix needs to know if a user is over quota so that it can reject further emails. That’s the purpose of the `quota-status` service which is now listening on TCP port 13373 (on the local interface) for such queries. The protocol is very simple and you can even play with it as a human:

Terminal window

    echo -e "recipient=john@example.org\n" | nc localhost 13373

And the service will respond with:

    action=OK

The response tells you whether the user is over quota:

- `action=OK` or
- `action=554 5.2.2 Quota exceeded (mailbox for user is full)`

## Postfix

Section titled “Postfix”

Telling Postfix to use the `quota-status` service is suprisingly simple:

Run this on your server

    postconf smtpd_recipient_restrictions="check_policy_service inet:localhost:13373"

Potential breakage with virtual_aliases

Do not use the `check_policy_service` if you are using virtual_aliases. See Julien’s comment. We need to find a solution for that.

### Test it

Section titled “Test it”

If you are curious to see this working, then set John’s mailbox quota to 5 KB:

    # mariadb mailservermysql> update virtual_users set quota=5120 where email='john@example.org';

Verify that he now has a limit of 5 KB:

Terminal window

    doveadm quota get -u john@example.org

Send him a few emails using the ‘swaks’ tool:

    swaks --server localhost --to john@example.org -tls

After a few emails you will see the rejection message:

    -> RCPT TO:john@example.org <** 452 4.2.2 john@example.org: Recipient address rejected: Mailbox is full and cannot receive any more emails

### Troubleshooting

Section titled “Troubleshooting”

These are things you should consider if quotas do not seem to work properly:

- Check that your `/etc/dovecot/conf.d/99-ispmail-sql.conf` file looks as described. Earlier version of this Trixie guide did not contain the `quota_storage_size` field in the `userdb sql` query.
- Run `tcpdump -Ai lo port 13373` on the server to see if Postfix talks to the `quota-status` service.
- Your users may complain that they have deleted many emails but are still over quota. Let them check if they actually emptied the Trash folder. Of course emails in that folder also contribute to the disk space usage. Once the Trash folder is expunged the problem should be gone. You may also allow your users more space in the Trash folder. That’s explained in the Dovecot documentation.
- If you directly remove files from a user’s Maildir instead of properly accessing the mailbox using IMAP then you will screw up the quota calculation. In that case let Dovecot recalculate the quota:
  `doveadm quota recalc -u john@example.org`

### See also

Section titled “See also”

- https://doc.dovecot.org/2.4.2/core/plugins/quota.html#quota-service
- https://sys4.de/en/blog/postfix-dovecot-mailbox-quota/
- https://www.postfix.org/SMTPD_POLICY_README.html