For the past two days, I've received about a dozen emails from zixcorp.com saying that some user had sent me a secure email and they want me to log in to retrieve it.
I don't recognize the address that they claim tried to send me the secure messge, so I've contacted both that address and support[at]zixcorp.com and asked them to stop sending me emails. There's no "unsubscribe" link in their email, which seems to violate CAN-spam?
To my surprise, within a day I got a reply from support[at]zixcorp.com, but they claim that they have no responsibility for the emails, nor do they have any way to stop them since they are "just a mail relay".
What recourse do I have to stop these emails beyond reporting them to Spamcop and emailing their upstream ISP?
Here's the original email I got from them (I received dozens, each similar):
Here is their support engineer's reply:
Here's partial mail headers from the original email I received from them: