Groupon UK Breached

Two days ago I got a very suspicious email on one of my accounts. (Probably) like many people I operate a domain purely for emails and I like to have a catch all on said domain so I can label my emails when signing up for things and keep track of who has my email. For example lets say I signed up to hacker news I might use the email address "ycombinator2013@mydomain.com" - this allows me to know the source should one of these companies get hacked or sell my data on. I only use the email addresses to signup to things and NEVER use the same email twice on 2 different sites and the email address never EVER gets given to anyone. Also because it's a catchall it goes to my main email account in Winblows mail so hitting "Reply" makes it come from my SINGLE outbound smtp email account (i/e not from "ycombinator2013@mydomain.com") IF and when I ever do reply to emails.

As I already stated A couple of days ago I received an email to "groupon2012email@mydomain.com" which was odd as this is the first time it had ever happened. I proceeded to get in contact with Groupon who flat out told me that "You mustv'e given the email out to a third party" - which I know to be false else what ever would be the point in myself tracking signups by using non generic emails?

I'll update this as and when they get back to me again :)