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Table of Contents
Ubuntu - Email - Install Dovecot
Dovecot is an IMAP server.
It takes responsibility for connecting your email client (Thunderbird, etc.) to your mail box.
Dovecot is configured to provide authentication (username and password) support to Postfix that is used when an authorized user goes to send email via Postfix.
NOTE: Your email client will connect to Dovecot using a protocol called IMAP (or POP).
Dovecot provides access to your mailboxes and when you are reading your email you are using Dovecot.
When you to go send mail from your email client, it connects directly to Postfix using a protocol called SMTP. Dovecot is not needed here.
However, before you can be allowed to access your email you need to prove that you are authorized to access it. This is referred to as authentication. To support this, Dovecot provides support for authentication.
In the earlier simpler days of the Internet before Spam, authentication was not required to send email. However these days you also need to authenticate yourself to prove that you are authorized to send mail. Sending mail is handled by Postfix, but rather than building authentication into Postfix as well, Postfix is instead configured to use Dovecot for authentication when sending email.
Install Dovecot
sudo apt install dovecot
Configuring Dovecot
The configuration files for Dovecot are usually found in /etc/dovecot.
NOTE: It is recommended to leave the default configuration alone and just adding your modifications into local.conf.
This file is read last and so any settings it contains will override the same settings that are contained in the default configuration.
Basic Configuration
The first part of the configuration specifies which protocols to support (IMAP and/or POP3) and where the mailboxes can be found:
- /etc/dovecot/local.conf
#protocols = imap pop3 protocols = imap mail_location = maildir:~/mail
Transport Layer Security (SSL)
This assumes that you have already created an certificate using OpenSSL. The one I am using is named ssl-mail-cert:
- /etc/dovecot/local.conf
... # TLS/SSL protocols to use (avoid older SSL protocols) ssl_protocols = !SSLv2 !SSLv3 # SSL ciphers to use ssl_cipher_list = ALL:!ADH:!EXPORT:!SSLv2:!aNULL:!eNULL:RC4+RSA:+HIGH:-MEDIUM:-LOW ssl_prefer_server_ciphers = yes # SSL certificate ssl=required ssl_cert = </etc/pki/tls/certs/ssl-mail-cert.crt ssl_key = </etc/pki/tls/private/ssl-mail-cert.key
Authentication
The following is used to configure authentication:
- /etc/dovecot/local.conf
... auth_mechanisms = plain passdb { driver = passwd-file args = /etc/dovecot/passwd } userdb { driver = static args = uid=vmail gid=vmail home=/home/vmail/%d/%n allow_all_users=yes } service auth { unix_listener auth-client { path = /var/spool/postfix/private/auth mode = 0660 user = postfix group = postfix } user = root }
NOTE:
- auth_mechanisms specifies the various forms in which the password can be passed to Dovecot (there may be more than one specified).
- Using plain is fine because it will only be passed through an SSL tunnel, and so will not be exposed.
- passdb specifies password database, in this case /etc/dovecot/passwd. It takes the form:
- /etc/dovecot/passwd
peter@sharewiz.net:{PLAIN}5Eu6f9AKe2vN peter@abcd.com:{PLAIN}L2YoWQ6JdSCo admin@sharewiz.net:{PLAIN}M2ydCc4ZwA1s
- Each consists of the email for each of the virtual mail boxes (much match values given to Postfix in the virtual_mailbox_maps file).
- After the email address there is a colon and then a specification of how the password is encoded enclosed in braces.
- Finally there is the encoded password. Of course, if the encoding is specified as PLAIN, there is no encoding and the password is given directly. However it is more secure it you do encode the passwords. To do so, run:
doveadm pw -s SSHA- SSHA employs a salted SSH1 hash, but there are many others available.
- userdb specifies parameters used when creating the virtual mailboxes.
- service auth specifies the parameters for a socket that is created to allow Postfix to communicate with Dovecot to support authentication.
- The path is the location of the socket (the last part of this path should be specified to Postfix in smtpd_sasl_path.