Sendmail smart relay with TLS and plain auth

Instructions on how I set up sendmail smart relay with TLS and plain authenetication on CentOS 6.

First, make sure you have enough installed :

yum -y install ca-certificates sendmail sendmail-cf

Create /etc/mail/authinfo:

AuthInfo:YOUR.HOST.COM    "U:YOUR-USER@YOUR.HOST.COM" "I:YOUR-USER" "P:YOUR-PASSWORD" "M:LOGIN PLAIN"

Replace YOUR.HOST.COM, YOUR-USER and YOUR-PASSWORD with the correct stuff. LOGIN PLAIN stays as-is if you are using plaintext logins. Make sure to chmod 0600 this file.

Add the following to /etc/mail/sendmail.mc, making sure you use m4's dumbass `quotation' style

define(`SMART_HOST', `YOUR.HOST.COM')dnl
define(`RELAY_MAILER',`esmtp')dnl
define(`RELAY_MAILER_ARGS', `TCP $h 587')dnl
FEATURE(`authinfo')dnl
define(`confCACERT_PATH', `/etc/pki/tls/certs')dnl
define(`confCACERT', `/etc/pki/tls/certs/ca-bundle.crt')dnl

Note that the above is TCP port 587, which you might need to change.

Finally you restart sendmail and test as you normally woudl.

chmod 0600 /etc/mail/authinfo
service sendmail restart
echo "Testing" | mail -s "Test 1" somebody@example.com
tail -F /var/log/maillog

Postfix mail relaying

RHEL 6 (and CentOS) have moved from sendmail to postfix. This is for the most part a Good Thing; sendmail was a mess. However it means I have to learn some new stuff. Specifically, how to convince postfix to relay email through my ISP's SMTP server.

First, I have a VM that does relaying for all my other computers. On this VM, I set up postfix to relay all mail :

# /etc/postfix/main.cf
myorigin = awale.qc.ca
relayhost = smtp.cgocable.ca
inet_interfaces = all
mynetworks = 10.0.0.0/24, 127.0.0.0/8

myorigin means user@localhost becomes user@awale.qc.ca.

relayhost is where email is relayed to.

inet_interfaces means postfix will listen for SMTP on all the VMs networks (default is only localhost).

mynetworks means postfix will trust any email coming from a host on my LAN. Yes, this is not very secure. But I trust my LAN explicitly. I have Wifi on a separate subnet, so anything on my LAN will have to be physically connected to my LAN.

On other computers/VMs, I just need myorigin and relayhost. This last points to the postfix VM, not COGECO.