Postfix SMTP relayhost configuration

Recently I was working on setting up SMTP Authentication to send mails through there ISP's mail server.

I first tried with perl MIME::Lite program which i found very hard to work with SMTP Authentication. So I decided to configure Postfix to relay mails to ISP mail server ( with SMTP Authentiction).

Postfix main configuration file: /etc/postfix/main.cf

myhostname = localhost
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
mydestination = localhost, localhost.localdomain, localhost
relayhost = smtp.isp.com
mynetworks = 127.0.0.0/8
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = loopback-only
smtp_use_tls = yes
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/smtp_auth ## **
smtp_sasl_security_options = noanonymous

To check postfix config.

#postfix check
#postconf


** smtp_auth is the file we store Authentication information
smtp.isp.com sheeju@isp.com:mypassword

smtp_auth is in this format
***:password

*** - Depending on your provider this can be username or useremail.

Next create hash DB of smtp_auth.
#postmap hash:/etc/postfix/smtp_auth

otherwise you get the error..

postfix/smtp[nnnnn]: fatal: open database /etc/postfix/smtp_auth.db: No such file or directory

Restart Postfix

# /etc/init.d/postfix restart

Testing Postfix:

echo testing | mail -s Bla sheejuec7@gmail.com

This is used to send test mail to sheejuec7@gmail.com. Next to check whether the mail relayed through ISP use

mailq
tail /var/log/mail.log