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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. _________________________________________________________________________________ Thanks to http://techgurulive.com/2008/09/16/how-to-smart-host-sendmail/
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