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Use a bought SSL certificate

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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.

StartSSL.com offers free one-year certificate.

Generate SSL private key and buy one SSL certificate

First of all, you need to generate a new SSL certificate 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 server.key -out server.csr

This command will generate two files:

server.key: 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: server.key 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:

server.crt
server.ca-bundle

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

on RHEL/CentOS: server.crt and server.ca-bundle should be placed under /etc/pki/tls/certs/, server.key should be /etc/pki/tls/private/.
on Debian/Ubuntu, FreeBSD: server.crt and server.ca-bundle should be placed under /etc/ssl/certs/, server.key 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.

Postfix (SMTP server)

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

postconf -e smtpd_use_tls='yes'
postconf -e smtpd_tls_cert_file='/etc/pki/tls/certs/server.crt'
postconf -e smtpd_tls_key_file='/etc/pki/tls/private/server.key'
postconf -e smtpd_tls_CAfile='/etc/pki/tls/certs/server.ca-bundle'

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/server.crt
ssl_key = </etc/pki/tls/private/server.key
ssl_ca = </etc/pki/tls/certs/server.ca-bundle

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/server.crt
SSLCertificateKeyFile /etc/pki/tls/private/server.key
SSLCertificateChainFile /etc/pki/tls/certs/server.ca-bundle

Restarting Apache service is required.

Nginx (web server)

On Linux and OpenBSD, it's defined in /etc/nginx/conf.d/default.conf.
On FreeBSD, it's defined in /usr/local/etc/nginx/conf.d/default.conf.

server {
    listen 443;
    ...
    ssl on;
    ssl_certificate /etc/pki/tls/certs/server.crt;
    ssl_certificate_key /etc/pki/tls/private/server.key;
    ...
}

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 server.crt server.ca-bundle > 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.

Reference

Configuring HTTPS servers

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