Configure Gmail SMTP Relay

SMTP stands for Simple Mail Transfer Protocol, lets you send email messages through your email account using your existing email service. This email service is subject to your interest. It could be any like: Gmail Relay, Snail Mail etc.

In this post we are going to configure Gmail Relay to send emails.


Install Postfix and other required packages.
yum install postfix
yum install mail*
yum install libsasl2-modules*
yum install cyrus-sasl-lib.x86_64 cyrus-sasl-lib.i686 -y
yum install cyrus-sasl-plain -y

• Configure Postfix main configuration
  1. Open main configuration file in edit mode.
     vi /etc/postfix/main.cf
  2. Add these lines in main configuration file at the bottom:

     smtp_sasl_security_options =
     relayhost = [smtp.gmail.com]:587
     smtp_use_tls = yes
     smtp_tls_CAfile = /etc/postfix/cacert.pem
     smtp_sasl_auth_enable = yes
     smtp_sasl_password_maps = hash:/etc/postfix/sasl/passwd
     smtp_sasl_authentication_filter =
     

  3. Save and exit

• Create /etc/postfix/sasl/passwd
  1. Create a directory sasl under /etc/postfix and create a file passwd with contents below:
     [smtp.gmail.com]:587  username@gmail.com:password
     Save and exit
  2. Change permission
     chmod 600 /etc/postfix/sasl/passwd
  3. Create lookup table via postmap
     postmap /etc/postfix/sasl/passwd
     Issuing that command will create passwd.db 

• Generate your own CA certificate
  1. Change directory to /etc/pki/tls/certs
     cd /etc/pki/tls/certs
  2. Create a key and test certificate in one file
     make hostname.pem
     You will something like
     

     [root@ip-10-112-95-49]# make hostname.pem
     
     umask 77 ; \
     PEM1='/bin/mktemp /tmp/openssl.XXXXXX' ; \
     PEM2='/bin/mktemp /tmp/openssl.XXXXXX' ; \
     /usr/bin/openssl req -utf8 -newkey rsa:1024 -keyout $PEM1 -nodes -x509 -days 365 -out $PEM2 -set_serial 0 ; \
     cat $PEM1 >  hostname.pem ; \
     echo ""    >> hostname.pem ; \
     cat $PEM2 >> hostname.pem ; \
     rm -f $PEM1 $PEM2
     Generating a 1024 bit RSA private key
     ……………………….++++++
     …..++++++
     writing new private key to ‘/tmp/openssl.z12084'
     —– 
     You are about to be asked to enter information that will be incorporated 
     into your certificate request.
     What you are about to enter is what is called a Distinguished Name or a DN.
     There are quite a few fields but you can leave some blank
     For some fields there will be a default value,
     If you enter ‘.’, the field will be left blank.
     —–
     Country Name (2 letter code) [GB]:
     State or Province Name (full name) [Berkshire]:
     Locality Name (eg, city) [Newbury]:
     Organization Name (eg, company) [My Company Ltd]:
     Organizational Unit Name (eg, section) []:
     Common Name (eg, your name or your server's hostname) []:
     Email Address []:
     

  3. Fill-up the necessary information and copy the file on /etc/postfix as cacert.pem
     cp /etc/pki/tls/certs/hostname.pem /etc/postfix/cacert.pem 

• Restart the postfix service

service postfix restart 

• Inspect now your postfix logs to see if it can send out mails now to gmail servers

  A successful message states something like [[BR]]
  May  3 17:35:00 FLT postfix/smtp[28244]: 0ABB61CE32A: to=, relay=smtp.gmail.com[74.125.93.109]:587, delay=5, delays=0.41/0.02/2.7/1.8, dsn=2.0.0, status=sent (250 2.0.0 OK 1272879300 8sm8902550qwj.38)
  

Check Email functionality

To check that emails are working fine, use mail command.
mail -s subject recpientemailaddress
Example: mail -s "Email Notification" gaurav81083@gmail.com
.

Checking mail log

To check the mail logs, use tail command
tail -f /var/log/maillog