Had no idea mailchimp does that. I mean I never used it myself for sending but I may have used it in the past as subscriber somewhere. Seems like another good reason to do the extra work of adding a mail forwarder for each sign-on that want’s mail. Thanks for pointing this issue out!
I discovered a disturbing thing yesterday when exporting my Mailchimp e-mail contacts for IFF. Mailchimp has more personal data than I asked for