Fedora 9: Smart Host Sendmail HowTo

Sendmail can be configured to send emails directly to destination host or email server. However, network traffic congestion, email destination location, and connectivity rate sometimes affect and tend to fail a successful email delivery.

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

Minimum Requirements

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

define(`SMART_HOST', `you-smtp.your.provider')

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.