I keep dedicated email addresses for most purposes, and the two that are getting any are a random mailing list, and the kickstarter address. That one has been caught in a vortex of spam, clearly meaning that kickstarter can't keep their mouths shut about customer emails.
Most of it goes to:
* admin@<mydomain>.com - listed in whois publicly for a few years, understandable
* <dropbox's address>@<mydomain.com> - started coming in 2014, the fact they were breached only became properly known in 2016.
* <my first name>@<mydomain.com> - This is the actual email address I give to in person contacts. Not quite sure how it ended up on spam lists, my best guesses are from a recruiter sharing it, git commits (though the fact the address I use way more commonly for git isn't there indicates probably not) or someone just figured it out.