Please correct me if I'm wrong, but I don't think anything was being sent to that mailinator address.

From looking at both that source code and emails received by my users, the mailinator address seems to be only in the message header "to" field, which, AFAIK, doesn't do anything other than display in the mail client.

The actual recipient's address is in the envelope recipient field.

I don't understand what the purpose of that mailinator address was.

It sends an email to that mailinator address, with all of the contacts BCC'd. mailinator shut it down very quickly but emails definitely went to that address.