Forking external binaries

Hello All, I was hoping to benefit from the collective wisdom of the list. We have a web application that forks off an external program to inject an email in the outgoing queue. At busy periods this external program (qmail-inject) can take a little while to return. I'm currently using popen() to spawn the qmail-inject binary. Is there a way to spawn the external binary but not wait for it to return. I'd be happy to ignore any return value if the tradeoff was a fast return. Suggestions or advice would be most welcome. Best regards, Mark.