If you are using Sendmail as your email server you can improve your deliverability by configuring a Turbo SMTP Smart host relay service. You’ll be recognized as a reliable email sender and protect yourself against identity theft. Here is the path you have to follow to set up our smart host smtp relay service in Sendmail:
First, set your access credentials /etc/mail/access
AuthInfo:pro.turbo-smtp.com "U:yourUserName" "P:yourPassword" "M:PLAIN"
In /etc/mail/sendmail.mc, after the first line (#dnl define(‘SMART_HOST’, ‘smtp.your.provider’)dnl), set your Smart Host definition:
define(`SMART_HOST', `pro.turbo-smtp.com')dnl FEATURE(`access_db')dnl define(`RELAY_MAILER_ARGS', `TCP $h 587')dnl define(`ESMTP_MAILER_ARGS', `TCP $h 587')dnl
To complete the procedure, update sendmail.cf and access.db files. Note: you will have to execute these commands as ‘su’ or ‘root’
$ cd /etc/mail $ m4 sendmail.mc >sendmail.cf $ makemap hash access < access
Finally restart Sendmail following the path that matches your Sendmail version:
For older versions:
$ /etc/init.d/sendmail restart
For newer versions:
$ service sendmail restart