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Sendmail over SSL (TLS) Encryption
First you need to create the server's SSL certificate.
cd /usr/share/ssl/certs
make sendmail.pem
Configure the sendmail.mc file to support SMTP over SSL (TLS).
vi /etc/mail/sendmail.mc
#---
define(`confCACERT_PATH',`/usr/share/ssl/certs')
define(`confCACERT',`/usr/share/ssl/certs/ca-bundle.crt')
define(`confSERVER_CERT',`/usr/share/ssl/certs/sendmail.pem')
define(`confSERVER_KEY',`/usr/share/ssl/certs/sendmail.pem')
DAEMON_OPTIONS(`Port=smtps, Name=TLSMTA, M=s')dnl
#---
Compiled the sendmail.cf file and restart Sendmail services.
m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf
service sendmail restart
If you run the iptables firewall, open the necessary hole.
vi /etc/sysconfig/iptables
#---
-A [name] -m state --state NEW -m tcp -p tcp --dport 465 -j ACCEPT
#---
service iptables restart
You can now send your SMTP emails securely with SSL encryption.
Although keep in mind this only guarantees an SSL connection between
your client and server. If you want to guarantee encryption
between SMTP servers, further Sendmail configuration is necessary.
- Scotech
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