docker-mailserver/docs/content/config/advanced/auth-ldap.md

---
title: 'Advanced | LDAP Authentication'
---

## Introduction

Getting started with ldap and `docker-mailserver` we need to take 3 parts in account:

- `postfix` for incoming & outgoing email
- `dovecot` for accessing mailboxes
- `saslauthd` for SMTP authentication (this can also be delegated to dovecot)

## Variables to Control Provisioning by the Container

Have a look at [the ENV page][docs-environment] for information on the default values.

### `LDAP_QUERY_FILTER_*`

Those variables contain the LDAP lookup filters for postfix, using `%s` as the placeholder for the domain or email address in question. This means that...

- ...for incoming email, the domain must return an entry for the `DOMAIN` filter (see [`virtual_alias_domains`](http://www.postfix.org/postconf.5.html#virtual_alias_domains)).
- ...for incoming email, the inboxes which receive the email are chosen by the `USER`, `ALIAS` and `GROUP` filters.
    - The `USER` filter specifies personal mailboxes, for which only one should exist per address, for example `(mail=%s)` (also see [`virtual_mailbox_maps`](http://www.postfix.org/postconf.5.html#virtual_mailbox_maps))
    - The `ALIAS` filter specifies aliases for mailboxes, using [`virtual_alias_maps`](http://www.postfix.org/postconf.5.html#virtual_alias_maps), for example `(mailAlias=%s)`
    - The `GROUP` filter specifies the personal mailboxes in a group (for emails that multiple people shall receive), using [`virtual_alias_maps`](http://www.postfix.org/postconf.5.html#virtual_alias_maps), for example `(mailGroupMember=%s)`.
    - Technically, there is no difference between `ALIAS` and `GROUP`, but ideally you should use `ALIAS` for personal aliases for a singular person (like `ceo@example.org`) and `GROUP` for multiple people (like `hr@example.org`).
- ...for outgoing email, the sender address is put through the `SENDERS` filter, and only if the authenticated user is one of the returned entries, the email can be sent.
    - This only applies if `SPOOF_PROTECTION=1`.
    - If the `SENDERS` filter is missing, the `USER`, `ALIAS` and `GROUP` filters will be used in in a disjunction (OR).
    - To for example allow users from the `admin` group to spoof any sender email address, and to force everyone else to only use their personal mailbox address for outgoing email, you can use something like this: `(|(memberOf=cn=admin,*)(mail=%s))`

???+ example

    A really simple `LDAP_QUERY_FILTER` configuration, using only the _user filter_ and allowing only `admin@*` to spoof any sender addresses.

    ```yaml
    - ENABLE_LDAP=1
    - LDAP_SERVER_HOST=ldap.example.org
    - LDAP_SEARCH_BASE=dc=example,dc=org"
    - LDAP_BIND_DN=cn=admin,dc=example,dc=org
    - LDAP_BIND_PW=mypassword
    - SPOOF_PROTECTION=1
    
    - LDAP_QUERY_FILTER_DOMAIN=(mail=*@%s)
    - LDAP_QUERY_FILTER_USER=(mail=%s)
    - LDAP_QUERY_FILTER_ALIAS=(|) # doesn't match anything
    - LDAP_QUERY_FILTER_GROUP=(|) # doesn't match anything
    - LDAP_QUERY_FILTER_SENDERS=(|(mail=%s)(mail=admin@*))
    ```

### `DOVECOT_*_FILTER` & `DOVECOT_*_ATTRS`

These variables specify the LDAP filters that dovecot uses to determine if a user can log in to their IMAP account, and which mailbox is responsible to receive email for a specific postfix user.

This is split into the following two lookups, both using `%u` as the placeholder for the full login name ([see dovecot documentation for a full list of placeholders](https://doc.dovecot.org/configuration_manual/config_file/config_variables/)). Usually you only need to set `DOVECOT_USER_FILTER`, in which case it will be used for both filters.

- `DOVECOT_USER_FILTER` is used to get the account details (uid, gid, home directory, quota, ...) of a user.
- `DOVECOT_PASS_FILTER` is used to get the password information of the user, and is in pretty much all cases identical to `DOVECOT_USER_FILTER` (which is the default behaviour if left away).

If your directory doesn't have the [postfix-book schema](https://github.com/variablenix/ldap-mail-schema/blob/master/postfix-book.schema) installed, then you must change the internal attribute handling for dovecot. For this you have to change the `pass_attr` and the `user_attr` mapping, as shown in the example below:

```yaml
- DOVECOT_PASS_ATTRS=<YOUR_USER_IDENTIFIER_ATTRIBUTE>=user,<YOUR_USER_PASSWORD_ATTRIBUTE>=password
- DOVECOT_USER_ATTRS=<YOUR_USER_HOME_DIRECTORY_ATTRIBUTE>=home,<YOUR_USER_MAILSTORE_ATTRIBUTE>=mail,<YOUR_USER_MAIL_UID_ATTRIBUTE>=uid,<YOUR_USER_MAIL_GID_ATTRIBUTE>=gid
```

!!! note

    For `DOVECOT_*_ATTRS`, you can replace `ldapAttr=dovecotAttr` with `=dovecotAttr=%{ldap:ldapAttr}` for more flexibility, like for example `=home=/var/mail/%{ldap:uid}` or just `=uid=5000`.

    A list of dovecot attributes can be found [in the dovecot documentation](https://doc.dovecot.org/configuration_manual/authentication/user_databases_userdb/#authentication-user-database).

???+ example "Defaults"

    ```yaml
    - DOVECOT_USER_ATTRS=mailHomeDirectory=home,mailUidNumber=uid,mailGidNumber=gid,mailStorageDirectory=mail
    - DOVECOT_PASS_ATTRS=uniqueIdentifier=user,userPassword=password
    - DOVECOT_USER_FILTER=(&(objectClass=PostfixBookMailAccount)(uniqueIdentifier=%n))
    ```

???+ example

    Setup for a directory that has the [qmail-schema](https://github.com/amery/qmail/blob/master/qmail.schema) installed and uses `uid`:

    ```yaml
    - DOVECOT_PASS_ATTRS=uid=user,userPassword=password
    - DOVECOT_USER_ATTRS=homeDirectory=home,qmailUID=uid,qmailGID=gid,mailMessageStore=mail
    - DOVECOT_USER_FILTER=(&(objectClass=qmailUser)(uid=%u)(accountStatus=active))
    ```

The LDAP server configuration for dovecot will be taken mostly from postfix, other options can be found in [the environment section in the docs][docs-environment].

### `DOVECOT_AUTH_BIND`

Set this to `yes` to enable authentication binds ([more details in the dovecot documentation](https://wiki.dovecot.org/AuthDatabase/LDAP/AuthBinds)). Currently, only DN lookup is supported without further changes to the configuration files, so this is only useful when you want to bind as a readonly user without the permission to read passwords.

### `SASLAUTHD_LDAP_FILTER`

This filter is used for `saslauthd`, which is called by postfix when someone is authenticating through SMTP (assuming that `SASLAUTHD_MECHANISMS=ldap` is being used). Note that you'll need to set up the LDAP server for saslauthd separately from postfix.

The filter variables are explained in detail [in the `LDAP_SASLAUTHD` file](https://github.com/winlibs/cyrus-sasl/blob/master/saslauthd/LDAP_SASLAUTHD#L121), but unfortunately, this method doesn't really support domains right now - that means that `%U` is the only token that makes sense in this variable.

!!! note "When to use this and how to avoid it"

    Using a separate filter for SMTP authentication allows you to for example allow `noreply@example.org` to send email, but not log in to IMAP or receive email: `(&(mail=%U@example.org)(|(memberOf=cn=email,*)(mail=noreply@example.org)))`

    If you don't want to use a separate filter for SMTP authentication, you can set `SASLAUTHD_MECHANISMS=rimap` and `SASLAUTHD_MECH_OPTIONS=127.0.0.1` to authenticate against dovecot instead - this means that the `DOVECOT_USER_FILTER` and `DOVECOT_PASS_FILTER` will be used for SMTP authentication as well.

???+ example "Configure LDAP with `saslauthd`"

    ```yaml
    - ENABLE_SASLAUTHD=1
    - SASLAUTHD_MECHANISMS=ldap
    - SASLAUTHD_LDAP_FILTER=(mail=%U@example.org)
    ```

## Secure Connection with LDAPS or StartTLS

To enable LDAPS, all you need to do is to add the protocol to `LDAP_SERVER_HOST`, for example `ldaps://example.org:636`.

To enable LDAP over StartTLS (on port 389), you need to set the following environment variables instead (the **protocol must not be `ldaps://`** in this case!):

```yaml
- LDAP_START_TLS=yes
- DOVECOT_TLS=yes
- SASLAUTHD_LDAP_START_TLS=yes
```

## Active Directory Configurations (Tested with Samba4 AD Implementation)

In addition to LDAP explanation above, when Docker Mailserver is intended to be used with Active Directory (or the equivelant implementations like Samba4 AD DC) the following points should be taken into consideration:

- Samba4 Active Directory requires a **secure connection** to the domain controller (DC), either via SSL/TLS (LDAPS) or via StartTLS.
- The username equivalent in Active Directory is: `sAMAccountName`.
- `proxyAddresses` can be used to store email aliases of single users. The convention is to prefix the email aliases with `smtp:` (e.g: `smtp:some.name@example.com`).
- Active Directory is used typically not only as LDAP Directory storage, but also as a _domain controller_, i.e., it will do many things including authenticating users. Mixing Linux and Windows clients requires the usage of [RFC2307 attributes](https://wiki.samba.org/index.php/Administer_Unix_Attributes_in_AD_using_samba-tool_and_ldb-tools), namely `uidNumber`, `gidNumber` instead of the typical `uid`. Assigning different owner to email folders can also be done in this approach, nevertheless [there is a bug at the moment in Docker Mailserver that overwrites all permissions](https://github.com/docker-mailserver/docker-mailserver/pull/2256) when starting the container. Either a manual fix is necessary now, or a temporary workaround to use a hard-coded `ldap:uidNumber` that equals to `5000` until this issue is fixed.
- To deliver the emails to different members of Active Directory **Security Group** or **Distribution Group** (similar to mailing lists), use a [`user-patches.sh` script][docs-userpatches] to modify `ldap-groups.cf` so that it includes `leaf_result_attribute = mail` and `special_result_attribute = member`. This can be achieved simply by:

The configuration shown to get the Group to work is from [here](https://doc.zarafa.com/trunk/Administrator_Manual/en-US/html/_MTAIntegration.html) and [here](https://kb.kopano.io/display/WIKI/Postfix).

```
# user-patches.sh

...
grep -q '^leaf_result_attribute = mail$' /etc/postfix/ldap-groups.cf || echo "leaf_result_attribute = mail" >> /etc/postfix/ldap-groups.cf
grep -q '^special_result_attribute = member$' /etc/postfix/ldap-groups.cf || echo "special_result_attribute = member" >> /etc/postfix/ldap-groups.cf
...
```

- In `/etc/ldap/ldap.conf`, if the `TLS_REQCERT` is `demand` / `hard` (default), the CA certificate used to verify the LDAP server certificate must be recognized as a trusted CA. This can be done by volume mounting the `ca.crt` file and updating the trust store via a `user-patches.sh` script:

```
# user-patches.sh

...
cp /MOUNTED_FOLDER/ca.crt /usr/local/share/ca-certificates/
update-ca-certificates
...
```

The changes on the configurations necessary to work with Active Directory (**only changes are listed, the rest of the LDAP configuration can be taken from the other examples** shown in this documentation):

```
# If StartTLS is the chosen method to establish a secure connection with Active Directory.
- LDAP_START_TLS=yes
- SASLAUTHD_LDAP_START_TLS=yes
- DOVECOT_TLS=yes

- LDAP_QUERY_FILTER_USER=(&(objectclass=person)(mail=%s))
- LDAP_QUERY_FILTER_ALIAS=(&(objectclass=person)(proxyAddresses=smtp:%s))
# Filters Active Directory groups (mail lists). Additional changes on ldap-groups.cf are also required as shown above.
- LDAP_QUERY_FILTER_GROUP=(&(objectClass=group)(mail=%s))
- LDAP_QUERY_FILTER_DOMAIN=(mail=*@%s)
# Allows only Domain admins to send any sender email address, otherwise the sender address must match the LDAP attribute `mail`.
- SPOOF_PROTECTION=1
- LDAP_QUERY_FILTER_SENDERS=(|(mail=%s)(proxyAddresses=smtp:%s)(memberOf=cn=Domain Admins,cn=Users,dc=*))

- DOVECOT_USER_FILTER=(&(objectclass=person)(sAMAccountName=%n))
# At the moment to be able to use %{ldap:uidNumber}, a manual bug fix as described above must be used. Otherwise %{ldap:uidNumber} %{ldap:uidNumber} must be replaced by the hard-coded value 5000.
- DOVECOT_USER_ATTRS==uid=%{ldap:uidNumber},=gid=5000,=home=/var/mail/%Ln,=mail=maildir:~/Maildir
- DOVECOT_PASS_ATTRS=sAMAccountName=user,userPassword=password
- SASLAUTHD_LDAP_FILTER=(&(sAMAccountName=%U)(objectClass=person))
```

## LDAP Setup Examples

???+ example "Basic Setup"

    ```yaml
    version: '3.8'
    services:
      mailserver:
        image: docker.io/mailserver/docker-mailserver:latest
        container_name: mailserver
        hostname: mail
        domainname: example.com

        ports:
          - "25:25"
          - "143:143"
          - "587:587"
          - "993:993"

        volumes:
          - ./docker-data/dms/mail-data/:/var/mail/
          - ./docker-data/dms/mail-state/:/var/mail-state/
          - ./docker-data/dms/mail-logs/:/var/log/mail/
          - ./docker-data/dms/config/:/tmp/docker-mailserver/
          - /etc/localtime:/etc/localtime:ro

        environment:
          - ENABLE_SPAMASSASSIN=1
          - ENABLE_CLAMAV=1
          - ENABLE_FAIL2BAN=1
          - ENABLE_POSTGREY=1

          # >>> Postfix LDAP Integration
          - ENABLE_LDAP=1
          - LDAP_SERVER_HOST=ldap.example.org
          - LDAP_BIND_DN=cn=admin,ou=users,dc=example,dc=org
          - LDAP_BIND_PW=mypassword
          - LDAP_SEARCH_BASE=dc=example,dc=org
          - LDAP_QUERY_FILTER_DOMAIN=(|(mail=*@%s)(mailAlias=*@%s)(mailGroupMember=*@%s))
          - LDAP_QUERY_FILTER_USER=(&(objectClass=inetOrgPerson)(mail=%s))
          - LDAP_QUERY_FILTER_ALIAS=(&(objectClass=inetOrgPerson)(mailAlias=%s))
          - LDAP_QUERY_FILTER_GROUP=(&(objectClass=inetOrgPerson)(mailGroupMember=%s))
          - LDAP_QUERY_FILTER_SENDERS=(&(objectClass=inetOrgPerson)(|(mail=%s)(mailAlias=%s)(mailGroupMember=%s)))
          - SPOOF_PROTECTION=1
          # <<< Postfix LDAP Integration

          # >>> Dovecot LDAP Integration
          - DOVECOT_USER_FILTER=(&(objectClass=inetOrgPerson)(mail=%u))
          - DOVECOT_PASS_ATTRS=uid=user,userPassword=password
          - DOVECOT_USER_ATTRS==home=/var/mail/%{ldap:uid},=mail=maildir:~/Maildir,uidNumber=uid,gidNumber=gid
          # <<< Dovecot LDAP Integration

          # >>> SASL LDAP Authentication
          - ENABLE_SASLAUTHD=1
          - SASLAUTHD_MECHANISMS=ldap
          - SASLAUTHD_LDAP_FILTER=(&(mail=%U@example.org)(objectClass=inetOrgPerson))
          # <<< SASL LDAP Authentication

          - ONE_DIR=1
          - SSL_TYPE=letsencrypt
          - PERMIT_DOCKER=host

        cap_add:
          - NET_ADMIN
    ```

??? example "Kopano / Zarafa"

    ```yaml
    version: '3.8'

    services:
      mailserver:
        image: docker.io/mailserver/docker-mailserver:latest
        container_name: mailserver
        hostname: mail
        domainname: example.com

        ports:
          - "25:25"
          - "143:143"
          - "587:587"
          - "993:993"

        volumes:
          - ./docker-data/dms/mail-data/:/var/mail/
          - ./docker-data/dms/mail-state/:/var/mail-state/
          - ./docker-data/dms/config/:/tmp/docker-mailserver/

        environment:
          # We are not using dovecot here
          - SMTP_ONLY=1
          - ENABLE_SPAMASSASSIN=1
          - ENABLE_CLAMAV=1
          - ENABLE_FAIL2BAN=1
          - ENABLE_POSTGREY=1
          - SASLAUTHD_PASSWD=

          # >>> SASL Authentication
          - ENABLE_SASLAUTHD=1
          - SASLAUTHD_LDAP_FILTER=(&(sAMAccountName=%U)(objectClass=person))
          - SASLAUTHD_MECHANISMS=ldap
          # <<< SASL Authentication

          # >>> Postfix Ldap Integration
          - ENABLE_LDAP=1
          - LDAP_SERVER_HOST=<yourLdapContainer/yourLdapServer>
          - LDAP_SEARCH_BASE=dc=mydomain,dc=loc
          - LDAP_BIND_DN=cn=Administrator,cn=Users,dc=mydomain,dc=loc
          - LDAP_BIND_PW=mypassword
          - LDAP_QUERY_FILTER_USER=(&(objectClass=user)(mail=%s))
          - LDAP_QUERY_FILTER_GROUP=(&(objectclass=group)(mail=%s))
          - LDAP_QUERY_FILTER_ALIAS=(&(objectClass=user)(otherMailbox=%s))
          - LDAP_QUERY_FILTER_DOMAIN=(&(|(mail=*@%s)(mailalias=*@%s)(mailGroupMember=*@%s))(mailEnabled=TRUE))
          # <<< Postfix Ldap Integration

          # >>> Kopano Integration
          - ENABLE_POSTFIX_VIRTUAL_TRANSPORT=1
          - POSTFIX_DAGENT=lmtp:kopano:2003
          # <<< Kopano Integration

          - ONE_DIR=1
          - SSL_TYPE=letsencrypt
          - PERMIT_DOCKER=host

        cap_add:
          - NET_ADMIN
    ```

[docs-environment]: ../environment.md
[docs-userpatches]: ./override-defaults/user-patches.md