A most persistent spam, part III

Earlier this month I nuked two email addresses being spammed by Alekandr [1] and wanted to wait to see how things go. Two weeks later and Aleksandr (all “his” emails came from the same domain but from different subdomains) are still being sent, still being delayed by my greylist daemon [2] only to be rejected because the destination email address no longer exists. I'm surprised that they are still attempting to deliver the emails. Is it that Aleksandr doesn't care if the emails make it or not? I noticed that the IP (Internet Protocol) addresses are changing more often now—is it a test to see if the IP address being used is blocked? Is it a smear campaign against Aleksandr? What is the end game here?