Dovecot SSL configuration
=========================

The most important SSL settings are:

---%<-------------------------------------------------------------------------
# Make sure you have imaps and pop3s if you want to support them.
# It's also possible to only use STARTTLS/STLS commands in imap/pop3 port.
protocols = imap pop3 imaps pop3s

ssl_disable = no # v1.2.beta1+ uses ssl = yes
# Preferred permissions: root:root 0444
ssl_cert_file = /etc/ssl/certs/dovecot.pem
# Preferred permissions: root:root 0400
ssl_key_file = /etc/ssl/private/dovecot.pem
---%<-------------------------------------------------------------------------

The certificate file can be world-readable, since it doesn't contain anything
sensitive (in fact it's sent to each connecting SSL client). The key file's
permissions should be restricted to only root (and possibly ssl-certs group or
similar if your OS uses such). Dovecot opens both of these files while still
running as root, so you don't need to give Dovecot any special permissions to
read them (in fact:*do not give dovecot user any permissions to the key file*).

It's possible to keep the certificate and the key both in the same file:

---%<-------------------------------------------------------------------------
# Preferred permissions: root:root 0400
ssl_cert_file = /etc/ssl/dovecot.pem
ssl_key_file = /etc/ssl/dovecot.pem
---%<-------------------------------------------------------------------------

It's also possible to use different certificates for IMAP and POP3:

---%<-------------------------------------------------------------------------
protocol imap {
  ssl_cert_file = /etc/ssl/certs/imap.pem
  ssl_key_file = /etc/ssl/private/imap.pem
}
protocol pop3 {
  ssl_cert_file = /etc/ssl/certs/pop3.pem
  ssl_key_file = /etc/ssl/private/pop3.pem
}
---%<-------------------------------------------------------------------------

There are a couple of different ways to specify when SSL/TLS is required:

 * 'disable_plaintext_auth=yes' allows <plaintext authentication>
   [Authentication.Mechanisms.txt] only when SSL/TLS is used first.
 * 'ssl = required' (v1.2+) requires SSL/TLS also for <non-plaintext
   authentication> [Authentication.Mechanisms.txt].
 * If you have only plaintext mechanisms enabled ('auth { mechanisms = plain
   login }'), you can use either (or both) of the above settings. They behave
   exactly the same way then.

Multiple SSL certificates (v2.0+)
---------------------------------

---%<-------------------------------------------------------------------------
local imap.example.org {
  ssl_cert = </etc/ssl/certs/imap.example.org.crt
  ssl_key = </etc/ssl/private/imap.example.org.key
}
local imap.example2.org {
  ssl_cert = </etc/ssl/certs/imap.example2.org.crt
  ssl_key = </etc/ssl/private/imap.example2.org.key
}
# ..etc..
---%<-------------------------------------------------------------------------

With v1.x you need to use multiple instances with multiple configurations.

Password protected key files
----------------------------

SSL key files may be password protected. There are two ways to provide Dovecot
with the password:

 1. Starting Dovecot with 'dovecot -p' asks the password. It's not stored
    anywhere, so this method prevents Dovecot from starting automatically at
    startup.
 2. 'ssl_key_password' setting. Note that 'dovecot.conf' is by default
    world-readable, so you probably shouldn't place it there directly. Instead
    you could store it in a different file, such as '/etc/dovecot-private.conf'
    containing:

    ---%<---------------------------------------------------------------------
     ssl_key_password = secret
    ---%<---------------------------------------------------------------------

    and then use '!include_try /etc/dovecot-private.conf' in the main
    'dovecot.conf'.

Chained SSL certificates
------------------------

Put all the certificates in the 'ssl_cert_file' file. For example when using a
certificate signed by TDC the correct order is:

 1. Dovecot's public certificate
 2. TDC SSL Server CA
 3. TDC Internet Root CA
 4. Globalsign Partners CA

SSL security settings
---------------------

When Dovecot starts up for the first time, it generates new 512bit and 1024bit
Diffie Hellman parameters and saves them into
'<prefix>/var/lib/dovecot/ssl-parameters.ssl'. After the initial creation
they're by default regenerated every week. With newer computers the generation
shouldn't take more than a few seconds, but with older computers it can take as
long as half an hour. The extra security gained by the regeneration is quite
small, so with slower computers you might want to disable it:

---%<-------------------------------------------------------------------------
ssl_parameters_regenerate = 0
---%<-------------------------------------------------------------------------

By default Dovecot v1.1+ allows all except the "LOW" and SSLv2 ciphers. See
http://www.openssl.org/docs/apps/ciphers.html for a list of the ciphers.
Disallowing more won't really gain any security for those using better ciphers,
but it does prevent people from accidentally using insecure ciphers. You can
change the cipher list with:

---%<-------------------------------------------------------------------------
ssl_cipher_list = ALL:!LOW:!SSLv2
---%<-------------------------------------------------------------------------

SSL verbosity
-------------

---%<-------------------------------------------------------------------------
verbose_ssl = yes
---%<-------------------------------------------------------------------------

This will make Dovecot log all the problems it sees with SSL connections. Some
errors might be caused by dropped connections, so it could be quite noisy.

Client certificate verification/authentication
----------------------------------------------

If you want to require clients to present a valid SSL certificate, you'll need
these settings:

---%<-------------------------------------------------------------------------
ssl_ca_file = /etc/ssl/ca.pem
ssl_verify_client_cert = yes

auth default {
  ssl_require_client_cert = yes
  #ssl_username_from_cert = yes
  ..
}
---%<-------------------------------------------------------------------------

The CA file should contain the certificate(s) followed by the matching CRL(s).
Note that the CRLs are required to exist. For a multi-level CA place the
certificates in this order:

 1. Issuing CA cert
 2. Issuing CA CRL
 3. Intermediate CA cert
 4. Intermediate CA CRL
 5. Root CA cert
 6. Root CA CRL

The certificates and the CRLs have to be in PEM format. To convert a DER format
CRL (e.g.http://crl.cacert.org/class3-revoke.crl) into PEM format, use:

---%<-------------------------------------------------------------------------
openssl crl -in class3-revoke.crl -inform DER -outform PEM > class3-revoke.pem
---%<-------------------------------------------------------------------------

With the above settings if a client connects which doesn't present a
certificate signed by one of the CAs in the 'ssl_ca_file', Dovecot won't let
the user log in.

You may also force the username to be taken from the certificate by setting
'ssl_username_from_cert = yes'.

 * The text is looked up from subject DN's specified field using OpenSSL's
   'X509_NAME_get_text_by_NID()' function.
 * By default the 'CommonName' field is used.
 * With v1.1.alpha5 and later you can change the field with
   'ssl_cert_username_field = name' setting (parsed using OpenSSL's
   'OBJ_txt2nid()' function). 'x500UniqueIdentifier' is a common choice.

You may also want to disable the password checking completely. Doing this
currently circumvents Dovecot's security model so it's not recommended to use
it, but it is possible by making the <passdb> [PasswordDatabase.txt] allow
logins using any password (typically requiring <"nopassword" extra field>
[PasswordDatabase.ExtraFields.txt] to be returned).

(This file was created from the wiki on 2010-05-24 04:42)
