To track the source of unsolicited emails I receive, I use a small trick. Every time I sign up on a website I add a + domain to my gmail address (you still receive the email).
Today I received a spam email from Groupon to email+ticketmaster@gmail.com. (screenshot - https://twitter.com/martindaniel4/status/917454181094453248)
That basically means that Ticketmaster sold my email to Groupon.
They both lost at least one customer.