Episode11: Can sendmail be used without DNS?

There are a number of steps required to successfully use sendmail when there is limited or no DNS.


•Setting a SMARTHOST

◦Ensure the required host is resolvable, either by /etc/hosts or DNS, or alternatively specify an IP address.

◦Use line in /etc/mail/sendmail.mc that resembles define(`SMART_HOST',`name.of.smart.host')dnl

•Since the system implicitly have limited resolving capabilities, accept email for unknown domains

◦Use line in /etc/mail/sendmail.mc of the form FEATURE(accept_unresolvable_domains)dnl

•Ensure that the ServiceSwitchFile (by default at /etc/mail/service.switch) has content similar to:


aliases files
hosts files


•Setting the submission agent to ignore DNS

◦Use line in /etc/mail/submit.mc of the form define(`confDIRECT_SUBMISSION_MODIFIERS',`C')

◦Use line in /etc/mail/submit.mc of the form FEATURE(accept_unresolvable_domains)dnl


Having completed the above changes remake the submit.cf & sendmail.cf by typing make in /etc/mail


The daemon may also need to be restarted with the command:




# service sendmail restart