# Dovecot

[TOC]

• Written for CentOS 7.1, Dovecot 2.2.10.
• Users are system users (in /etc/aliases)
• Mailbox style is Maildir (in their home folders.)
• Certificates are Comodo PositiveSSLs from NameCheap

## Pre-Flight

Getting your mail is not something which can always be done via telnet (insecure) or SSH (e.g. in the case of virtual accounts.)1 Dovecot allows you to get your mail using the POP3 and/or IMAP protocols.

### On SSL

• The Dovecot instance will use POP3S and IMAPS in addition to POP3 and IMAP. When TLS properly implemented/initiated with the latter pair, there’s really no reason why the former would be required. Seems to be some debate about this.
• The Comodo certificates were chosen since they would work with Gmail and most other MUAs.

## Installation

yum install dovecot
systemctl enable dovecot


## Configuration

Turn off SSL (for now) in /etc/dovecot/conf.d/10-ssl.conf.

ssl = no


### Initial Configuration

Edit /etc/dovecot/dovecot.conf and set the protocols you want to serve

protocols = imap pop3


Listen on IPv4 and IPv6 interfaces

listen = *, ::


Location for run time data

base_dir = /var/run/dovecot/


Now, in /etc/dovecot/conf.d/10-mail.conf, tell Dovecot where to find the messages

mail_location = maildir:~/Maildir


Start the service and make sure it’s running

[root@example ~]# systemctl start dovecot
[root@example ~]# netstat -tulpn | grep dovecot
tcp   0      0 0.0.0.0:110      0.0.0.0:*         LISTEN      7183/dovecot
tcp   0      0 0.0.0.0:143      0.0.0.0:*         LISTEN      7183/dovecot
tcp   0      0 :::110           :::*              LISTEN      7183/dovecot
tcp   0      0 :::143           :::*              LISTEN      7183/dovecot


### Testing

You can now telnet to either ports 110 (POP3) or 143 (IMAP). The syntaxes differ quite a bit.

Make sure firewall is poked :)

### Securing

Now we use TLS with the POP3 and IMAP ports. All authentication and message transfer will be done only over a secure connection.

Edit /etc/dovecot/conf.d/10-ssl.conf to mandate SSL

ssl = required


And configure the certificates and keys you will use

ssl_cert = </etc/pki/tls/certs/example.com.crt
ssl_key = </etc/pki/tls/private/example.com.key
ssl_ca = </etc/pki/CA/certs/ca-bundle.pem


Now disable plaintext authentication in /etc/dovecot/10-auth.conf

disable_plaintext_auth = yes


Restart the dovecot service. You’ll see ports 993 and 995 in the netstat output. Use OpenSSL to test the POP3S service first:

openssl s_client -connect example.com:995


You should be able to log in and check some test messages. The IMAP service should work fine as well.

Importantly, you should not be able to authenticate insecurely.

[root@example ~]# telnet example.com 110
Trying 96.126.123.32...
Connected to example.com.
Escape character is '^]'.
user testuser
-ERR Plaintext authentication disallowed on non-secure (SSL/TLS) connections.


This is good. Test like crazy!

### Other Notes

• When creating a CA bundle, go Root → Intermediate → Intermediate → … → Your Certificate.

• When connecting via OpenSSL, note how POP3 and IMAP servers respond (with the greeting “I am ready”):

  # IMAP
* OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE AUTH=PLAIN] I am ready.

# POP3