[Mail Servers] : How to configure Sendmail server in Red Hat Linux

Let me show you simple steps to configure a sendmail server which will use external smtp server to send mails across the network.

IMPORTANT NOTE:

Please make sure that this will NOT act as a smtp server instead it will send mails using smtp.gmail.com. You will be able to send mails on any address over the internet using your local linux box mail address but you won't be able to receive any of the mails from outside domain.

NOTE: This is a simple configuration but if you want to insert some special permissions and authentications let me know I will try to help with additional info.

To start of  with the configuration initially you need to check for the presence of STARTLS and SASLv2 in your machine.

# sendmail -d0.1 -bv root
Version 8.13.8
Compiled with: DNSMAP HESIOD HES_GETMAILHOST LDAPMAP LOG MAP_REGEX
MATCHGECOS MILTER MIME7TO8 MIME8TO7 NAMED_BIND NETINET NETINET6
NETUNIX NEWDB NIS PIPELINING SASLv2 SCANF SOCKETMAP STARTTLS 
TCPWRAPPERS USERDB USE_LDAP_INIT 
============ SYSTEM IDENTITY (after readcf) ============ 
(short domain name) $w = server 
(canonical domain name) $j = server.example.com 
(subdomain name) $m = example.com 
(node name) $k = server.example.com 
========================================================
# yum -y install sendmail
# rpm -qa | grep sendmail
sendmail-cf-8.13.8-2.el5
sendmail-8.13.8-2.el5
make sure that you install sendmail-cf because while mapping sendmail.mc into sendmail.cf you need sendmail-cf as mentioned in the configuration file


# vi /etc/mail/sendmail.mc
define(`SMART_HOST', `smtp.gmail.com')dnl 

# (add these two lines in your sendmail.mc file to listen on port 465 and 587)
define(`RELAY_MAILER_ARGS', `TCP $h 587')dnl 
define(`ESMTP_MAILER_ARGS', `TCP $h 587')dnl 

# uncomment this line
TRUST_AUTH_MECH(`EXTERNAL DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl
define(`confAUTH_MECHANISMS', `EXTERNAL GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl 

# add this line 
FEATURE(`authinfo', `hash /etc/mail/auth/client-info.db')dnl 
FEATURE(`access_db', `hash -T<TMPF> -o /etc/mail/access.db')dnl 
DAEMON_OPTIONS(`Port=smtp, Name=MTA')dnl 

# uncomment for sendmail to listen on port 587
DAEMON_OPTIONS(`Port=submission, Name=MSA, M=Ea')dnl 

# uncomment for sendmail to listen on port 587
DAEMON_OPTIONS(`Port=smtps, Name=TLSMTA, M=s')dnl 

# write your domain and uncomment
MASQUERADE_AS(`mydomain.com')dnl
Make a directory auth inside /etc/mail and assign proper permissions to auth so that no other user can access this directory
# mkdir /etc/mail/auth
# cd /etc/mail/auth
Create a new file client-info

# vi client-info
AuthInfo:gmail.com "U:username" "P:Password" "M:PLAIN"
AuthInfo: "U:username" "P:Password" "M:PLAIN
# makemap -r hash client-info.db < client-info
# vi /etc/mail/access
Connect:your-ip RELAY
# m4 sendmail.mc > sendmail.cf
# service sendmail restart
# sendmail -v user@domain.com
NOTE: If you get any error message or you are unable to send mails even after following the above configuration kindly revert back with the log messages so that I can help you further for the same.