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Use a SSL certificate

[TOC]

iRedMail generates a self-signed SSL certificate during installation, it's fine if you just want to secure the network connections (POP3/IMAP/SMTP over TLS, HTTPS), but mail clients or web browsers will promot a annoying message to warn you this self-signed certificate is not trusted. To avoid this annoying message, you have to buy a SSL certificate from SSL certificate provider. Search buy ssl certificate in Google will give you many SSL providers, choose the one you prefer.

Get a SSL certificate

Get a free LetsEncrypt ssl cert

"Let's Encrypt" offers free SSL certificate, please follow its official tutorial to get one: https://certbot.eff.org

!!! attention

The `--apache` option of `certbot` program will modify Apache config
files, most time it messes up iRedMail configurations, so it's better
to get the cert with `certonly --webroot` option while requesting cert, then
follow tutorial below to update config files to use the cert.

Buy from a trusted SSL vendor

To buy ssl cert from a trusted vendor, you need to generate a new SSL key and signing request file on your server with openssl command:

!!! warning

Do NOT use key length smaller than `2048` bit, it's insecure.

# openssl req -new -newkey rsa:2048 -nodes -keyout privkey.pem -out server.csr

This command will generate two files:

  • privkey.pem: the private key for the decryption of your SSL certificate.
  • server.csr: the certificate signing request (CSR) file used to apply for your SSL certificate. This file is required by SSL certificate provider.

The openssl command will prompt for the following X.509 attributes of the certificate:

  • Country Name (2 letter code): Use the two-letter code without punctuation for country. for example: US, CA, CN.
  • State or Province Name (full name): Spell out the state completely; do not abbreviate the state or province name, for example: California.
  • Locality Name (eg, city): City or town name, for example: Berkeley.
  • Organization Name (eg, company): Your company name.
  • Organizational Unit Name (eg, section): The name of the department or organization unit making the request.
  • Common Name (e.g. server FQDN or YOUR name): server FQDN or your name.
  • Email Address []: your full email address.
  • A challenge password []: type a password for this ssl certificate.
  • An optional company name []: an optional company name.

NOTE: Some certificates can only be used on web servers using the Common Name specified during enrollment. For example, a certificate for the domain domain.com will receive a warning if accessing a site named www.domain.com or secure.domain.com, because www.domain.com and secure.domain.com are different from domain.com.

Now you have two files: privkey.pem and server.csr. Go to the website of your preferred SSL privider, it will ask you to upload server.csr file to issue an SSL certificate.

Usually, SSL provider will give you 2 files:

  • cert.pem
  • fullchain.pem (some SSL providers use name server.ca-bundle)

We need above 2 files, and privkey.pem. Upload them to your server, you can store them in any directory you like, recommended directories are:

  • on RHEL/CentOS: cert.pem and fullchain.pem should be placed under /etc/pki/tls/certs/, privkey.pem should be /etc/pki/tls/private/.
  • on Debian/Ubuntu, FreeBSD: cert.pem and fullchain.pem should be placed under /etc/ssl/certs/, privkey.pem should be /etc/ssl/private/.
  • on OpenBSD: /etc/ssl/.

Configure Postfix/Dovecot/Apache/Nginx to use bought SSL certificate

We use CentOS for example in below tutorial, please adjust the file to correct one on your server according to above description.

Postfix (SMTP server)

We can use postconf command to update SSL related settings directly:

postconf -e smtpd_tls_cert_file='/etc/pki/tls/certs/cert.pem'
postconf -e smtpd_tls_key_file='/etc/pki/tls/private/privkey.pem'
postconf -e smtpd_tls_CAfile='/etc/pki/tls/certs/fullchain.pem'

Restarting Postfix service is required.

Dovecot (POP3/IMAP server)

SSL certificate settings are defined in Dovecot main config file, /etc/dovecot/dovecot.conf (Linux/OpenBSD) or /usr/local/etc/dovecot/dovecot.conf (FreeBSD):

ssl = required
ssl_cert = </etc/pki/tls/certs/cert.pem
ssl_key = </etc/pki/tls/private/privkey.pem
ssl_ca = </etc/pki/tls/certs/fullchain.pem

Restarting Dovecot service is required.

Apache (web server)

  • On RHEL/CentOS, SSL certificate is defined in /etc/httpd/conf.d/ssl.conf.
  • On Debian/Ubuntu, it's defined in /etc/apache2/sites-available/default-ssl (or default-ssl.conf)
  • On FreeBSD, it's defined in /usr/local/etc/apache24/extra/httpd-ssl.conf. Note: if you're running different version of Apache, the path will be slightly different (apache24 will be apache[_version_]).
  • On OpenBSD, if you're running OpenBSD 5.5 or earlier releases, it's defined in /var/www/conf/httpd.conf. Note: OpenBSD 5.6 and later releases don't ship Apache anymore.

Example:

SSLCertificateFile /etc/pki/tls/certs/cert.pem
SSLCertificateKeyFile /etc/pki/tls/private/privkey.pem
SSLCertificateChainFile /etc/pki/tls/certs/fullchain.pem

Restarting Apache service is required.

Nginx (web server)

  • On Linux and OpenBSD, it's defined in /etc/nginx/templates/ssl.tmpl (or /etc/nginx/conf.d/default.conf on old iRedMail release)
  • On FreeBSD, it's defined in /usr/local/etc/nginx/templates/ssl.tmpl (or /usr/local/etc/nginx/conf.d/default.conf on old iRedMail release)
ssl_certificate /etc/pki/tls/certs/cert.pem;
ssl_certificate_key /etc/pki/tls/private/privkey.pem;

Some browsers may complain about a certificate signed by a well-known certificate authority, while other browsers may accept the certificate without issues. This occurs because the issuing authority has signed the server certificate using an intermediate certificate that is not present in the certificate base of well-known trusted certificate authorities which is distributed with a particular browser. In this case the authority provides a bundle of chained certificates which should be concatenated to the signed server certificate. The server certificate must appear before the chained certificates in the combined file:

# cd /etc/pki/tls/certs/
# cat cert.pem fullchain.pem > server.chained.crt

Then update ssl_certificate parameter in /etc/nginx/conf.d/default.conf:

    ssl_certificate /etc/pki/tls/certs/server.chained.crt;

Restarting Nginx service is required.

MySQL, MariaDB

If MySQL/MariaDB is listening on localhost and not accessible from external network, this is OPTIONAL.

  • On Red Hat and CentOS, it's defined in /etc/my.cnf
  • On Debian and Ubuntu, it's defined in /etc/mysql/my.cnf.
    • Since Ubuntu 15.04, it's defined in /etc/mysql/mariadb.conf.d/mysqld.cnf.
  • On FreeBSD, it's defined in /usr/local/etc/my.cnf.
  • On OpenBSD, it's defined in /etc/my.cnf.
[mysqld]

ssl-ca = /etc/pki/tls/certs/fullchain.pem
ssl-cert = /etc/pki/tls/certs/cert.pem
ssl-key = /etc/pki/tls/private/privkey.pem

OpenLDAP

If OpenLDAP is listening on localhost and not accessible from external network, this is OPTIONAL.

  • On Red Hat and CentOS, it's defined in /etc/openldap/slapd.conf.
  • On Debian and Ubuntu, it's defined in /etc/ldap/slapd.conf.
  • On FreeBSD, it's defined in /usr/local/etc/openldap/slapd.conf.
  • On OpenBSD, it's defined in /etc/openldap/slapd.conf.
TLSCACertificateFile /etc/pki/tls/certs/fullchain.pem
TLSCertificateFile /etc/pki/tls/certs/cert.pem
TLSCertificateKeyFile /etc/pki/tls/private/privkey.pem

Restarting OpenLDAP service is required.

If you want to connect with TLS (port 389) or SSL (port 636) for secure connection from command line tools like ldapsearch, please update parameter TLS_CACERT in OpenLDAP client config file also, otherwise you will get error message like Peer's Certificate issuer is not recognized.

  • On Red Hat and CentOS, it's defined in /etc/openldap/ldap.conf.
  • On Debian and Ubuntu, it's defined in /etc/ldap/ldap.conf.
  • On FreeBSD, it's defined in /usr/local/etc/openldap/ldap.conf.
  • On OpenBSD, it's defined in /etc/openldap/ldap.conf.
TLS_CACERT /etc/pki/tls/certs/fullchain.pem

To connect with TLS, please run ldapsearch with argument -Z and use ldap://<your_server_name>:389 as ldap host. For example:

ldapsearch -x -W -Z \
    -H 'ldap://mail.example.com:389' \
    -D 'cn=vmail,dc=example,dc=com' \
    -b 'o=domains,dc=example,dc=com' mail
  • To connection with SSL, use ldaps://<your_server_name>:636 as ldap host. for example:
ldapsearch -x -W \
    -H 'ldaps://mail.example.com:636' \
    -D 'cn=vmail,dc=example,dc=com' \
    -b 'o=domains,dc=example,dc=com' mail

OpenBSD ldapd(8)

If ldapd(8) is listening on localhost and not accessible from external network, this is OPTIONAL.

For more details about ldapd config file, please check its manual page: ldapd.conf(5).

To make ldapd(8) listening on network interface for external network, please make sure you have setting in /etc/ldapd.conf to listen on the interface. We use em0 as external network interface here for example.

# Listen on network interface 'em0', port 389, use STARTTLS for secure connection.
listen on em0 port 389 tls

If you want to use port 636 with SSL, try this:

# Listen on network interface 'em0', port 636, use SSL for secure connection.
listen on em0 port 636 ldaps

ldapd(8) will look for SSL cert and key from directory /etc/ldap/certs/ by default, the cert file name is <interface_name>.crt and <interface_name>.key. In our case, it will look for /etc/ldap/certs/em0.crt and /etc/ldap/certs/em0.key.

Since iRedMail already generates a cert and key, we can use it directly. If you have bought SSL cert/key, or requested one from LetsEncrypt, you can use them too.

cd /etc/ldap/certs/
ln -s /etc/ssl/iRedMail.crt em0.crt
ln -s /etc/ssl/iRedMail.key em0.key

Now restart ldapd(8) service:

rcctl restart ldapd

Reference