Lets encrypt certifcate generation for centos postfix server

1. Install lets encrypt
2. yum -y install letsencrypt

Generate Lets encrypt certificate

1. letsencrypt certonly --standalone -d {domain name}

Main configuration file where we provide location to certificate

1. vi /etc/postfix/main.cf

Parameters that is added to postfix file

1. smtpd_tls_CAfile = /etc/letsencrypt/live/{domain name}/fullchain.pem
2. smtpd_tls_key_file =  /etc/letsencrypt/live/{domain name}/privkey.pem
3. smtpd_tls_cert_file = /etc/letsencrypt/live/{domain name}/cert.pem
4. smtpd_use_tls = yes

Package required for configuring auto renew of lets encrypt certificate 

1. wget https://dl.eff.org/certbot-auto && chmod a+x certbot-auto
2. mv certbot-auto /etc/letsencrypt/

Scheduling autorenew of Certificate

We need to renew it every 90 days

1. crontab -e

0 0 1 */2 * cd /etc/letsencrypt/ && ./certbot-auto renew 

0 0 1 */2 * cd /etc/letsencrypt/ && ./certbot-auto renew >/var/log/letsencrypt/letsencrypt.log 2>&1

Testing new certificate generation without overriding old one 

1. cd /etc/letsencrypt/ && ./certbot-auto renew --dry-run

Log of Lets encrypt 

1. cat /var/log/letsencrypt/letsencrypt.log