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113 lines
4.0 KiB
Markdown
113 lines
4.0 KiB
Markdown
---
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title: 'Use Cases | Forward-Only Mail-Server with LDAP'
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---
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## Building a Forward-Only Mail-Server
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A **forward-only** mail-server does not have any local mailboxes. Instead, it has only aliases that forward emails to external email accounts (for example to a Gmail account). You can also send email from the localhost (the computer where `docker-mailserver` is installed), using as sender any of the alias addresses.
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The important settings for this setup (on `mailserver.env`) are these:
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```env
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PERMIT_DOCKER=host
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ENABLE_POP3=
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ENABLE_CLAMAV=0
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SMTP_ONLY=1
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ENABLE_SPAMASSASSIN=0
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ENABLE_FETCHMAIL=0
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```
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Since there are no local mailboxes, we use `SMTP_ONLY=1` to disable `dovecot`. We disable as well the other services that are related to local mailboxes (`POP3`, `ClamAV`, `SpamAssassin`, etc.)
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We can create aliases with `./setup.sh`, like this:
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```sh
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./setup.sh alias add <alias-address> <external-email-account>
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```
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## Authenticating with LDAP
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If you want to send emails from outside the mail-server you have to authenticate somehow (with a username and password). One way of doing it is described in [this discussion][github-issue-1247]. However if there are many user accounts, it is better to use authentication with LDAP. The settings for this on `mailserver.env` are:
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```env
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ENABLE_LDAP=1
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LDAP_START_TLS=yes
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LDAP_SERVER_HOST=ldap.example.org
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LDAP_SEARCH_BASE=ou=users,dc=example,dc=org
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LDAP_BIND_DN=cn=mailserver,dc=example,dc=org
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LDAP_BIND_PW=pass1234
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ENABLE_SASLAUTHD=1
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SASLAUTHD_MECHANISMS=ldap
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SASLAUTHD_LDAP_SERVER=ldap.example.org
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SASLAUTHD_LDAP_START_TLS=yes
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SASLAUTHD_LDAP_BIND_DN=cn=mailserver,dc=example,dc=org
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SASLAUTHD_LDAP_PASSWORD=pass1234
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SASLAUTHD_LDAP_SEARCH_BASE=ou=users,dc=example,dc=org
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SASLAUTHD_LDAP_FILTER=(&(uid=%U)(objectClass=inetOrgPerson))
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```
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My LDAP data structure is very basic, containing only the username, password, and the external email address where to forward emails for this user. An entry looks like this:
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```properties
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add uid=username,ou=users,dc=example,dc=org
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uid: username
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objectClass: inetOrgPerson
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sn: username
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cn: username
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userPassword: {SSHA}abcdefghi123456789
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email: external-account@gmail.com
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```
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This structure is different from what is expected/assumed from the configuration scripts of `docker-mailserver`, so it doesn't work just by using the `LDAP_QUERY_FILTER_...` settings. Instead, I had to use a custom configuration ([via `user-patches.sh`][docs-userpatches]). I created the script `docker-data/dms/config/user-patches.sh`, with content like this:
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```bash
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#!/bin/bash
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rm -f /etc/postfix/{ldap-groups.cf,ldap-domains.cf}
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postconf \
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"virtual_mailbox_domains = /etc/postfix/vhost" \
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"virtual_alias_maps = ldap:/etc/postfix/ldap-aliases.cf texthash:/etc/postfix/virtual" \
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"smtpd_sender_login_maps = ldap:/etc/postfix/ldap-users.cf"
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sed -i /etc/postfix/ldap-users.cf \
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-e '/query_filter/d' \
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-e '/result_attribute/d' \
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-e '/result_format/d'
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cat <<EOF >> /etc/postfix/ldap-users.cf
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query_filter = (uid=%u)
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result_attribute = uid
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result_format = %s@example.org
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EOF
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sed -i /etc/postfix/ldap-aliases.cf \
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-e '/domain/d' \
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-e '/query_filter/d' \
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-e '/result_attribute/d'
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cat <<EOF >> /etc/postfix/ldap-aliases.cf
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domain = example.org
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query_filter = (uid=%u)
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result_attribute = mail
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EOF
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postfix reload
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```
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You see that besides `query_filter`, I had to customize as well `result_attribute` and `result_format`.
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!!! note "See also"
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For more details about using LDAP see: [LDAP managed mail-server with Postfix and Dovecot for multiple domains](https://www.vennedey.net/resources/2-LDAP-managed-mail-server-with-Postfix-and-Dovecot-for-multiple-domains)
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!!! note
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Another solution that serves as a forward-only mail-server is [this](https://gitlab.com/docker-scripts/postfix).
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!!! tip
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One user reports only having success if `ENABLE_LDAP=0` was set.
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[docs-userpatches]: ../../config/advanced/override-defaults/user-patches.md
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[github-issue-1247]: https://github.com/docker-mailserver/docker-mailserver/issues/1247
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