I started doing this, maybe 15 years ago, but if I look through my spam folder now, most of it is to the email address I used before I began using unique addresses (the rest is to random addresses in my domains that I've never used).

My hypotheses from that are that

• there is probably less 'selling of email lists' going on than we think
• I'm less interested in dubious internet sites than I used to be
• or (most likely) these days, your internet thing has to be offering me some real value if I'm going to consciously give you any of my data.

Not all providers let you use your own domain.

But then you need to do spam filtering for ages