Civimail delivering AND bouncing at the same time - what's missing?
Figured it out finally: bad default setting in php.ini. 

The isp had this param added by default: mail.force_extra_parameters adding "SMTP = smtp.myisp.net" to every outgoing mail sent by mail(). 

This caused every email to bounce when civi called qmail. 

Sheesh. I want those two days back.