# Request a free cert from Let's Encrypt (for servers deployed with downloadable iRedMail installer)

Attention

This tutorial is for servers deployed with downloadable iRedMail installer, if you're looking for tutorial for servers deployed with iRedMail Easy platform, plase check this one instead.

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 software 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, unless it's also a web host name.

### One cert for all domain names, or one cert for each domain name?

Dovecot and Nginx support reading/loading multiple ssl certs (for different host names), but old Postfix software doesn't, 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 you actually own or control the domain name.

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 cert

- Install the `certbot` package first:

  - on CentOS/Rocky/AlmaLinux: `yum install -y certbot` (offered by EPEL repo)
  - on Debian/Ubuntu: `apt install -y certbot`

- Let's Encrypt has request rate limit control, you can request limited times for same domain in one day, but the verification process doesn't have such limit. We suggest run verification process first to make sure we fully match its requirements.

  Run command below as root user to verify the request process with `--dry-run` argument. It will print some text on console to ask you few simple questions, please read carefully and answer them.

    certbot certonly --webroot --dry-run -w /opt/www/well_known -d mail.mydomain.com

    If you need to support multiple domain names in one cert, please append them
    with `-d` arguments like this:

    certbot certonly --webroot --dry-run \
        -w /opt/www/well_known \
        -d mail.mydomain.com \
        -d 2nd-domain.com \
        -d 3rd-domain.com \
        -d 4th-domain.com

- If everything went well and no error was reported by `certbot` program on console, that means we fully match the requirements, and it's ok to actually request the cert by running above command again but without `--dry-run` argument:

    certbot certonly --webroot -w /opt/www/well_known -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:

- `cert.pem`: Server certificate.
- `chain.pem`: Additional intermediate certificate or certificates that web browsers will need in order to validate the server certificate.
- `fullchain.pem`: All certificates, including server certificate (aka leaf certificate or end-entity certificate). The server certificate is the first one in this file, followed by any intermediates.
- `privkey.pem`: Private key for the certificate.

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}

## 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 to load the cert files.

- On RHEL/CentOS:

    mv /etc/pki/tls/certs/iRedMail.crt{,.bak}       # Backup
    mv /etc/pki/tls/private/iRedMail.key{,.bak}     # Backup
    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

- On Debian/Ubuntu, FreeBSD and OpenBSD:

    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

Now restart Postfix / Dovecot / Nginx services to use the cert:

    systemctl restart postfix dovecot nginx

### Verify the cert

- To verify ssl cert used in Postfix (SMTP server) and Dovecot, please launch a mail client application (MUA, e.g. Outlook, Thunderbird) and create an email account, make sure you correctly configured the MUA to connect to mail server. If SSL cert is not valid, MUA will warn you.
- For Apache / Nginx web server, you can access your website with favourite web browser, the browser should show you the ssl cert status. Or, use other website to help test it, for example: https://www.ssllabs.com/ssltest/index.html (input your web host name, then submit and wait for a result).

## Renew the cert automatically

Cert can be renewed manually with command `certbot renew`, or run same command in a daily or weekly cron job to renew automatically. Only those certs which expires in less than 30 days will be renewed. Applications use ssl cert must be restarted to load renewed cert files.

If cert was renewed, private key `/etc/letsencrypt/live/<domain>/privkey.pem` is re-created and linked to file under `/etc/letsencrypt/archive/<domain>/privkey<X>.pem` (`<X>` is a digit number), but all files linked to `/etc/letsencrypt/live/<domain>/privkey.pem` were left to the old one, so we must update all files linked to `/etc/letsencrypt/live/<domain>/privkey.pem` with argument `--post-hook` right after renewed to make sure they're linked to correct one.

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

Attention

- Replace `<domain>` by the real domain name.
- Replace `/etc/ssl/private/iRedMail.key` by the real linked private key file path on your server.
  - On CentOS/Rocky, it's `/etc/pki/tls/private/iRedMail.key`.
  - On Debian/Ubuntu, FreeBSD and OpenBSD, it's `/etc/ssl/private/iRedMail.key`.

    1 3 * * * certbot certificates; certbot renew --post-hook 'ln -sf /etc/letsencrypt/live/<domain>/privkey.pem /etc/ssl/private/iRedMail.key; /usr/bin/systemctl restart postfix dovecot nginx'

## Cert configuration in different applications

### 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

### 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.

- 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/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.

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

## References

- How it works

## See Also

- Request a free cert from Let's Encrypt (for servers deployed with iRedMail Easy platform)
- Use a bought SSL certificate