put & at the end of the sendmail command:
/usr/sbin/sendmail -bd -q1h &
this will start sendmil at the background. It can sit and try to resolve the domain name for few mintes but you will never know it.
© 2014, O’Reilly Media, Inc.
All trademarks and registered trademarks appearing on oreilly.com are the property of their respective owners.