Medium and large type of private networks are traditionally behind a firewall. This type of network usually sends emails directly to internal destination host and if all fails, elects a smart host, which is located outside their firewall, as their smart host email server to send emails to mostly external destination hosts. Having a smart host and gateway email server, relieves a lot of failing factors from sending emails directly from source to external destination host.
Sendmail provides a quick and simple method of configuring a smart host. Here’s a quick run down on how to configure your sendmail to act as smart host.
Configure Sendmail as Smart Host
1. Fedora or Linux Box
2. Existing and Working Sendmail Setup
3 .Existing DNS Setup
Configuration Steps for Sendmail as Smart Host
To create a smart host from your sendmail, backup and edit your sendmail conf file
# vi /etc/mail/sendmail.cdf
Look for sendmail directive line similar below and modify it
dnl define(`SMART_HOST’, `smtp.your.provider’)dnl
Simply replace ‘smtp.your.provider’ with your email gateway server and remove the starting and ending ‘dnl’ words from the line . The new sendmail smart host directive will look like
Save and exit.
Recompile sendmail configuration file
# m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf
Restart sendmail daemon service
# service sendmail restart
When an email failed to be delivered, sendmail smart host will act as a fallback failover mechanism on sending failed emails from local sendmail source to smart host STMP server then going to email destination server.