Postfix TLS

Configuring Postfix to use TLS on CentOS 7

1. Install all required packages
yum install cyrus-sasl cyrus-sasl-devel cyrus-sasl-gssapi cyrus-sasl-md5 cyrus-sasl-plain postfix

1b. Backup default postfix config
cp /etc/postfix/main.cf /etc/postfix/main.cf_orig

2. Configure SMTP-AUTH and TLS using postconf

/usr/sbin/postconf -e 'smtpd_sasl_local_domain =fqdn.com'
/usr/sbin/postconf -e 'smtpd_sasl_auth_enable = yes'
/usr/sbin/postconf -e 'smtpd_sasl_security_options = noanonymous'
/usr/sbin/postconf -e 'broken_sasl_auth_clients = yes'
/usr/sbin/postconf -e 'smtpd_recipient_restrictions = permit_mynetworks,permit_sasl_authenticated,reject_unauth_destination'
/usr/sbin/postconf -e 'inet_interfaces = all'
/usr/sbin/postconf -e 'mynetworks = 127.0.0.0/8, 10.0.0.0/8, 192.168.1.0/24, 192.168.100.0/24'

3. Set postfix to allow LOGIN and PLAIN logins.

vim /etc/sasl2/smtpd.conf

pwcheck_method: saslauthd
mech_list: plain login

4. Create key for SSL certificate signing request

mkdir /etc/postfix/ssl
cd /etc/postfix/ssl/
openssl genrsa -des3 -rand /etc/hosts -out smtpd.key 1024
chmod 600 smtpd.key

openssl req -new -key smtpd.key -out smtpd.csr

6. Create the SSL certificate with the signing request and the key

openssl x509 -req -days 3650 -in smtpd.csr -signkey smtpd.key -out smtpd.crt

7. Create RSA key

openssl rsa -in smtpd.key -out smtpd.key.unencrypted
mv smtpd.key.unencrypted smtpd.key

8. Create CA key and cert

openssl req -new -x509 -extensions v3_ca -keyout cakey.pem -out cacert.pem -days 3650

9. Configure postfix for TLS

/usr/sbin/postconf -e 'smtpd_tls_auth_only = no'
/usr/sbin/postconf -e 'smtp_use_tls = yes'
/usr/sbin/postconf -e 'smtpd_use_tls = yes'
/usr/sbin/postconf -e 'smtp_tls_note_starttls_offer = yes'
/usr/sbin/postconf -e 'smtpd_tls_key_file = /etc/postfix/ssl/smtpd.key'
/usr/sbin/postconf -e 'smtpd_tls_cert_file = /etc/postfix/ssl/smtpd.crt'
/usr/sbin/postconf -e 'smtpd_tls_CAfile = /etc/postfix/ssl/cacert.pem'
/usr/sbin/postconf -e 'smtpd_tls_loglevel = 1'
/usr/sbin/postconf -e 'smtpd_tls_received_header = yes'
/usr/sbin/postconf -e 'smtpd_tls_session_cache_timeout = 3600s'
/usr/sbin/postconf -e 'tls_random_source = dev:/dev/urandom'

10. Set servers hostname and mydomain in postfix config

/usr/sbin/postconf -e 'myhostname = host.yourdomain.com'
/usr/sbin/postconf -e 'mydomain = yourdomain.com'

11. Check through the postfix config to verify all of the settings.

more /etc/postfix/main.cf

12. Stop sendmail and Start postfix, saslauthd

systemctl stop sendmail 
systemctl restart postfix 
systemctl restart saslauthd