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# Dovecot

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Note Dovecot is available in two lines: 2.4 and 2.3. This article is about the most recent release, but some parts may still refer to the older versions.

Dovecot is an open source IMAP and POP3 server for Linux/UNIX-like systems, written primarily with security in mind. Dovecot primarily aims to be a lightweight, fast and easy to set up open source mailserver. For more detailed information, please see the official Dovecot documentation.

This article describes how to set up Dovecot for personal or small office use.

Due to breaking changes in Dovecot's configuration format in version 2.4, Arch Linux offers both the latest release and one from the 2.3 line. The latter will not receive any new features or bug fixes, other than critical security updates.

## Installation

Install the dovecot package for the most recent Dovecot version, or dovecot23 for the legacy 2.3 line.

## Configuration

Note

- In Dovecot 2.4 the configuration syntax has changed considerably from 2.3 and earlier versions (breaking changes!). Configuration files from before 2.4 are no longer supported. If you are upgrading from a pre-2.4-version, you have to rewrite your configuration.

- Mind that the migration can become challenging. Do not approach it lightly. The migration guide is terse, as the rest of Dovecot's documentation. Take your time. Make yourself comfortable with the subject. Most likely, you will have to go through a process of trial and error. If possible set up a testing environment that you can play around with. In the mean time consider using dovecot23 for your production environment.

Dovecot configuration is stored in `/etc/dovecot/dovecot.conf`. An example file is shipped with the package. To use the example config a few manual steps are still necessary:

- A `vmail` user and group needs to be created
- SSL certificate is necessary or needs to be created

See the official documentation TLDR and SSL and Plaintext Authentication for more information.

On top of that, the developers translated legacy examples to 2.4 syntax and offer them on GitHub. The examples are provided in hope they are helpful, but the archive is not expected to be kept up to date.

### Required settings

`dovecot_config_version` must be set and it has to be the first setting in the configuration file. `dovecot_storage_version` also has to be set. The values of these settings should match actually used configuration syntax, names, and formats of files created by Dovecot itself.

### Authentication

User authentication is managed through the `passdb` filters.

To enable PAM passdb driver:

    passdb pam {
        # Additional PAM-specific settings here, if needed.
    }

The associated PAM configuration is included in `/etc/pam.d/dovecot`.

See passdb documentation for other drivers and the list of their settings.

### TLS connections

To accept TLS connections, you need to obtain a certificate. This section assumes you already own one, together with the private key. Both must be in the PEM format.

First, generate parameters required for Diffie-Hellman key exchange:

    $ openssl dhparam -out dhparams.pem 4096

This operation may take some time. The output goes to `dhparams.pem`.

Finally, configure Dovecot to use all three files:

    ssl_server {
        cert_file = /path/to/fullchain.pem
        key_file = /path/to/privkey.pem
        dh_file = /path/to/dhparams.pem
    }

## Full Text Search

By default Dovecot does not index the full message content, which will result in slow response times for `IMAP SEARCH` queries for bigger mailboxes. There are a number of FTS backends Dovecot can be hooked up to.

Dovecot needs a plugin for the chosen search backend. The solr plugin is included in dovecot but solr itself is not the easiest to set up. There are packages for Xapian (dovecot-fts-xapian) and Elasticsearch (dovecot-fts-elastic).

## Starting the server

Start/enable `dovecot.service`.

## Tips and tricks

Generate hashes with non-default hash functions:

    $ doveadm pw -s SHA512-CRYPT -p "password"

Ensure that the column in the database is large enough. A warning will be emitted if it is too small.

Remember to set the password password scheme:

    dovecot-sql.conf

    default_pass_scheme = SHA512-CRYPT

## Troubleshooting

### warning: pipe flag `D' requires dovecot_destination_recipient_limit = 1

If you cannot receive emails with multiple recipients and there is something like this is your logs:

    mail postfix/pipe[663]: 72A62733: to=<user2@example.com>, relay=dovecot, delay=495, delays=495/0.01/0/0.08, dsn=4.3.5, status=deferred (mail system configuration error)
    mail postfix/pipe[663]: 72A62733: to=<user1@example.com>, relay=dovecot, delay=495, delays=495/0.01/0/0.06, dsn=4.3.5, status=deferred (mail system configuration error)
    mail postfix/pipe[1614231]: warning: pipe flag `D' requires dovecot_destination_recipient_limit = 1

Add `dovecot_destination_recipient_limit = 1` to `/etc/postfix/main.cf` and reload postfix.

### dovecot.service does not start after updating to 2.4

Dovecot 2.4 has introduced changes to the configuration files format and variable names. You need to translate your 2.3 configuration to make it compatible with 2.4. See #Configuration for more information.

As a temporary solution dovecot23 may be installed instead of dovecot.

### Dovecot and Postfix: cannot read SSL private key

If running dovecot 2.4 you encounter errors when running "any" dovecot executable as user, such as:

    Fatal: Error in configuration file /etc/dovecot/dovecot.conf line 80: cert_file: open(/etc/letsencrypt/live/server.tld/fullchain.pem) failed: Permission denied

This is a known issue, since "deliver" has to be able to read every configuration. But running `/usr/lib/dovecot/deliver` as user is useful, with procmail for instance.

To avoid the problem, dovecot provides a silently failing "include_try" mechanism, that you can use to make file unreadable to user but still enabling root to read SSL keys.

1. Create `/etc/dovecot/dovecot-ssl.conf` that contains the content of `ssl_server {...}` (above defined), something like:

    cert_file = /path/to/fullchain.pem
    key_file = /path/to/privkey.pem
    dh_file = /path/to/dhparams.pem

2. Prevent any user but "root" to read this file:

    chmod 600 /etc/dovecot/dovecot-ssl.conf

3. Replace the ssl_server part of `dovecot.conf` with this:

    ssl_server {
       !include_try /etc/dovecot/dovecot-ssl.conf
    }

4. (to test) The `doveconf` command should print your "certs_file" lines as root (with your private keys listed) and not be listed as unprivileged user.

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