Setting up SendMail as SMTP Relay Server

Here are the steps to take in order to use Sendmail as SMTP relay server:

By default relay on sendmail is disabled.

So when you do relay on it by doing telnet

220 nagios.gowireless.net ESMTP Sendmail 8.13.8/8.13.8; Fri, 29 Apr 2011 11:59:2
3 -0700
HELO
501 5.0.0 HELO requires domain address
MAIL FROM:test@test.com
250 2.1.0 test@test.com... Sender ok
relaying denied

So to allow relay on SendMail do as follows:

1. First allow the sendmail to listen to all at port 25. (Allow incoming smtp connections)

- Edit /etc/mail/sendmail.mc

Change...

DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')dnl

To..

DAEMON_OPTIONS(`Port=smtp, Name=MTA')dnl

- save it

and then do

make -C /etc/mail

- restart sendmail service

service sendmail restart

2. Allow or open port 25 on the firewall.

3. Now we will include IP based authentication

- Edit /etc/mail/access and add the IP / IP block to allow relay from

Connect:localhost.localdomain RELAY
Connect:localhost RELAY
Connect:127.0.0.1 RELAY
Connect:10.1 RELAY
Connect:1.1 RELAY

- save it

- then recompile the access.db

makemap hash /etc/mail/access.db < /etc/mail/access

- then do restart sendmail

4. To test do as follow from a different pc

telnet 10.1.10.13 25
220 nagios.gowireless.net ESMTP Sendmail 8.13.8/8.13.8; Fri, 29 Apr 2011 11:59:2
3 -0700
HELO
501 5.0.0 HELO requires domain address
MAIL FROM:test@test.com
250 2.1.0 test@test.com... Sender ok
RCPT TO:rowell.rufino@gowireless.com
250 2.1.5 rowell.rufino@gowireless.com... Recipient ok
DATA
354 Enter mail, end with "." on a line by itself
testing
.
250 2.0.0 p3TIxNH1002876 Message accepted for delivery
quit
221 2.0.0 nagios.gowireless.net closing connection

Hopefully you find this helpful. Thanks. Take Care and God Bless!!!