I just checked the spam folder of a gmail account I used for dropbox. Throughout the years I'd ocasionally (maybe once every two months or so) check the spam folder merely out of curiosity, but it was practically always empty.

Perhaps this is just a huge coincidence but I see three spam emails sent today plus another two sent this week. Some of them have cc recipients which seem legit addresses of other people, but I can't identify them. I never used Zendesk by the way.

Edit: here are the senders, in case it helps: no-reply@adsl.hu, no-reply@velkommenhit.no, no-reply@wdl.fr, no-reply@tataidc.co.in, no-reply@variationfm.com. Though it looks like these addresses may have been spoofed... the sender name is "{%FROM_NAME%}" in all of them.

Edit 2: It turns out Groupon Germany (former citydeal.de), which I checked out once with the same address, is responsible from what I can gather (link in german, but everything matches, company has yet to say anything): http://hukd.mydealz.de/diverses/groupon-verkauft-kundendaten...