Many years ago I created an email address to purchase things like software, amazon etc. I didn't want any spam in my personal email address. Years later I have yet to receive any spam in my "to purchase" address mail box. My personal email address mail box is filled with spam. My theory much of the spam comes from emails with a cc instead of a bcc and friends who went on web pages and put in my personal email address so I can get too good to believe deals, greeting cards etc.

There are lots of places where email addresses can be picked up by spammers. Most legitimate companies are safe, however, which explains your good experience with the purchasing address. The only trouble there would be a disgruntled employee stealing and reselling a list of addresses.