Has anyone considered the possibility - remote as it might seem due to the likelihood of the proffered answers being correct - that the emails are originating from DB6's computer, created by a spambot?
Possible, yes, remote, yes.
There was a time when spammers would pick an address at random as the "from" in their junk - and the poor unsuspecting owner would get thousands of "bounce" messages as a result. I don't know if that still happens, but I've not been drowned in bounces for a year or two.
Two possible reasons for the reduction in bounce messages for spam with faked From addresses:
- more people are configuring their mail servers not to send bounce messages in respect of obvious spam as, clearly, the bounce messages are of no use to anyone and just add to the problem
- more people are putting more sophisticated spam filtering on their incoming email, so the spam filtering might be throwing the bounce messages out as spam.