Since I run my own mailserver, I can put in filters to give errors out at the SMTP level (rather than bounces), so I have stuff like this in my access file for

Since I run my own mailserver, I can put in filters to give errors out at the SMTP level (rather than bounces), so I have stuff like this in my access file for egregious spammers (from legit companies): <some_email> ERROR:550 You've been banned from sending spam to this address, spamming bastard!! There's a whole bunch and the swearing ramps up and down based on the egregiousness of the spamming. I have no idea if anyone has ever seen these messages (probably not), but I really hope some day someone does :-). And yeah, swearing at spambots is oddly cathartic.