qmail auth smtp

I have received a number of emails over the past few months regarding adding a section on how to install auth smtp for qmail. To be quite honest, I haven't had the time to figure out how to do this. Plus, with my now 12 domains and 50 some users humming along beautifully on my current qmail server, I am very nervous about changing anything. (In fact, I'm downright paranoid about making any major changes - things have been smooth for 2 years now!) If anyone, however, knows how to add auth smtp to qmail as I have it installed, without hosing the current setup, I would appreciate the insight. A link to my address is in the nav bar above. Or, simply add comments to this posting... I'll see them in due time.