Request a free cert from Let's Encrypt

Attention

Check out the lightweight on-premises email archiving software developed by iRedMail team: Spider Email Archiver.

iRedMail generates a self-signed SSL certificate during installation, it's strongly recommended to use a valid ssl cert.

You can either request free cert, or buy one from ssl cert vendors. In this tutorial, we will show you how to request a free cert for host name mail.mydomain.com from Let's Encrypt, and ssl related configurations in relevant softwares running on iRedMail server.

Let's Encrypt supports wildcard host names, but it's not covered in this tutorial, please read its User Guide instead.

We use Let's Encrypt official tool named certbot to request cert, there're some other third-party tools you can use. On OpenBSD, you can use command acme-client which is in base system (check its manual page here: acme-client(1). To get a list of other tools, please visit Let's Encrypt website: ACME Client Implementations.

Before requesting a cert

Which host names should be supported in the SSL cert?

You must understand which host names you need to support in the SSL cert:

  1. The full hostname of your mail server.

    Server hostname is usually used as SMTP/IMAP/POP3 server address in user's mail client application like Outlook, Thunderbird.

    You can get full hostname with command hostname -f on Linux, or hostname on OpenBSD.

  2. The web host names you need to access via https.

    For example, https://mydomain.com, https://support.mydomain.com, then you need to support both mydomain.com and support.mydomain.com in ssl cert.

  3. NO need to support mail domain name in SSL cert, except it's a web host name also.

One cert for all host names, or one cert for each host name?

Dovecot and Nginx support reading/loading multiple ssl certs (for different host names), but Postfix doesn't (except running multiple Postfix instances and each instance uses one (different) ssl cert). so we recommend to use one cert for all host names which are used by SMTP and IMAP/POP3 services.

Make sure you have correct DNS record for the host names

The way we request free Let's Encrypt cert requires correct A type DNS record for the host name, because Let's Encrypt organization needs to make sure that you actually control the domain name and server. We will describe the detail later.

To check the DNS record, you can use dig command like below:

dig +short -t a mail.mydomain.com

It should return the (public) IP address of your server.

Request a free cert from Let's Encrypt

certbot certonly --webroot --dry-run -w /var/www/html -d mail.mydomain.com

What's happening after you typed this command? you may ask.

Things happening right behind the command

  1. certbot program creates a temporary plain text file locally under /var/www/html/.well-known/acme-challenge/. We use file name 35c9406f6b63bd18fa626e5bd9d0ea8b for example in this tutorial (/var/www/html/.well-known/acme-challenge/35c9406f6b63bd18fa626e5bd9d0ea8b).
  2. certbot program sends the request to Let's Encrypt organization's server, including the temporary file name.
  3. Let's Encrypt organization's server will perform http request to your server by visiting URL http://mail.mydomain.com/.well-known/acme-challenge/35c9406f6b63bd18fa626e5bd9d0ea8b to make sure the file actually exist on your server. This step is used to verify A type DNS record of the host name and the domain name ownership (you actually control this domain name and server).
  4. certbot program remove temporary file locally.
  5. if no error was reported by certbot program on console, and you run above command without --dry-run argument (described later in this tutorial), certbot will obtain ssl cert files and store them under /etc/letsencrypt/ directory.

For more details, please read Let's Encrypt official document: How it works.

Warning

We assume the web document root directory for web host name mail.mydomain.com is /var/www/html (this is default path configured by iRedMail downloadable installer). In new iRedMail releases, the path /.well-known/ is defined in Nginx config file /etc/nginx/templates/misc.tmpl, if you have hard-coded directory for it with Nginx directive root /path/to/somewhere;, you need to replace /var/www/html by /path/to/somewhere in commands. For example:

certbot certonly --webroot -w /path/to/somewhere -d mail.mydomain.com

And sample Nginx configuration:

location ~ ^/.well-known/ { allow all; root /path/to/somewhere; }

certbot certonly --webroot -w /var/www/html -d mail.mydomain.com

If the command finished successfully, it will create and store cert files under /etc/letsencrypt/live/mail.mydomain.com/ (You may have different host name instead of mail.mydomain.com in this sample path).

Created cert files:

Directory /etc/letsencrypt/live/ and /etc/letsencrypt/archive are owned by root user and group, with permission 0700 (set by certbot program) by default, it means other users can not access them -- including the daemon users used to run network services like Postfix/Dovecot/OpenLDAP/MariaDB/PostgreSQL. It's necessary to set the permission to 0755 for other applications to access them.

chmod 0755 /etc/letsencrypt/{live,archive}

Renew the cert automatically

You can setup a daily cron job to run command certbot renew to renew all existing ssl certs which will expire in less than 30 days. We need its --post-hook argument to restart network services to load renewed ssl certs.

A sample cron job that runs at 3:01AM everyday, and restart postfix/nginx/dovecot after renewed:

1   3   *   *   *   certbot renew --post-hook '/usr/sbin/service postfix restart; /usr/sbin/service nginx restart; /usr/sbin/service dovecot restart'

Use Let's Encrypt cert

The easiest and quickest way to use Let's Encrypt cert is creating symbol links to the self-signed SSL cert generated by iRedMail installer, then restart services which use the cert files.

For servers deployed with iRedMail Easy platform

If you deployed iRedMail with the iRedMail Easy platform, ssl cert/key files are:

Run commands below on RHEL/CentOS/Debian/Ubuntu/OpenBSD:

Attention

Please replace <domain> in sample commands below by the real domain name on your file system.

cd /opt/iredmail/ssl/
mv cert.pem cert.pem.bak
mv key.pem key.pem.bak
mv combined.pem combined.pem.bak
ln -s /etc/letsencrypt/live/<domain>/fullchain.pem combined.pem
ln -s /etc/letsencrypt/live/<domain>/fullchain.pem cert.pem
ln -s /etc/letsencrypt/live/<domain>/privkey.pem key.pem

If cert was renewed, /etc/letsencrypt/live/<domain>/privkey.pem will be re-created (it's a symbol link too), and it causes /opt/iredmail/ssl/key.pem linked to file under /etc/letsencrypt/archive/, so we need to update the --post-hook in cron job also:

Attention

Replace <domain> by the real domain name.

1 3 * * * certbot renew --post-hook 'ln -sf /etc/letsencrypt/live/<domain>/privkey.pem /opt/iredmail/ssl/key.pem; /usr/sbin/service postfix restart; /usr/sbin/service nginx restart; /usr/sbin/service dovecot restart'

For servers deployed with the classical downloadable iRedMail installer

mv /etc/pki/tls/certs/iRedMail.crt{,.bak}       # Backup. Rename iRedMail.crt to iRedMail.crt.bak
mv /etc/pki/tls/private/iRedMail.key{,.bak}     # Backup. Rename iRedMail.key to iRedMail.key.bak
ln -s /etc/letsencrypt/live/mail.mydomain.com/fullchain.pem /etc/pki/tls/certs/iRedMail.crt
ln -s /etc/letsencrypt/live/mail.mydomain.com/privkey.pem /etc/pki/tls/private/iRedMail.key
mv /etc/ssl/certs/iRedMail.crt{,.bak}       # Backup. Rename iRedMail.crt to iRedMail.crt.bak
mv /etc/ssl/private/iRedMail.key{,.bak}     # Backup. Rename iRedMail.key to iRedMail.key.bak
ln -s /etc/letsencrypt/live/mail.mydomain.com/fullchain.pem /etc/ssl/certs/iRedMail.crt
ln -s /etc/letsencrypt/live/mail.mydomain.com/privkey.pem /etc/ssl/private/iRedMail.key

Restart network services

Required services:

Depends on the backend you chose during iRedMail installation, you may need to restart:

Verify the cert

FAQ

Renew the cert

Let's Encrypt cert will expire in 90 days, you must renew it before expired. After renewed, don't forget to restart Postfix/Dovecot/Nginx/Apache to load the new cert files.

For more details, please read Let's Encrypt official document: Renewing certificates.

How to check cert status

Run command:

certbot certificates

It will show you all existing certs and expiry date.

How to request one cert with multiple host names

If you need to support multiple host names, you can specify multiple -w and -d arguments like below:

certbot certonly \
    --webroot \
    --dry-run \
    -w /var/www/html \
    -d mail.mydomain.com \
    -w /var/www/vhosts/2nd-domain.com \
    -d 2nd-domain.com \
    -w /var/www/vhosts/3rd-domain.com \
    -d 3rd-domain.com

SSL cert relevant settings in Postfix/Dovecot/Apache/Nginx

In sample settings below, file paths are for Debian/Ubuntu.

Postfix

File /etc/postfix/main.cf (on Linux/OpenBSD) or /usr/local/etc/postfix/main.cf (on FreeBSD):

smtpd_tls_cert_file = /etc/ssl/certs/iRedMail.crt
smtpd_tls_key_file = /etc/ssl/private/iRedMail.key
smtpd_tls_CAfile = /etc/ssl/certs/iRedMail.crt

Dovecot

File /etc/dovecot/dovecot.conf (on Linux/OpenBSD) or /usr/local/etc/dovecot/dovecot.conf (on FreeBSD):

ssl = required
ssl_cert = </etc/ssl/certs/iRedMail.crt
ssl_key = </etc/ssl/private/iRedMail.key
ssl_ca = </etc/ssl/certs/iRedMail.crt

Apache (web server)

Example:

SSLCertificateFile /etc/ssl/certs/iRedMail.crt
SSLCertificateKeyFile /etc/ssl/private/iRedMail.key
SSLCertificateChainFile /etc/ssl/certs/iRedMail.crt

Restarting Apache service is required.

Nginx

File /etc/nginx/templates/ssl.tmpl (on Linux/OpenBSD) or /usr/local/etc/nginx/templates/ssl.tmpl (on FreeBSD):

ssl_certificate /etc/ssl/certs/iRedMail.crt;
ssl_certificate_key /etc/ssl/private/iRedMail.key;

MySQL, MariaDB

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

[mysqld]

ssl-ca = /etc/ssl/certs/iRedMail.crt
ssl-cert = /etc/ssl/certs/iRedMail.crt
ssl-key = /etc/ssl/private/iRedMail.key

OpenLDAP

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

TLSCACertificateFile /etc/ssl/certs/iRedMail.crt
TLSCertificateKeyFile /etc/ssl/private/iRedMail.key
TLSCertificateFile /etc/ssl/certs/iRedMail.crt

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/letsencrypt/live/mail.mydomain.com/fullchain.pem em0.crt
ln -s /etc/letsencrypt/live/mail.mydomain.com/privkey.pem em0.key

Now restart ldapd(8) service:

rcctl restart ldapd

See Also