I sign-up for a service using "123abc-theirdomain.com@mydomain.com" as the email address. Messages to that address come to my "Inbox". I don't use the address f

I sign-up for a service using "123abc-theirdomain.com@mydomain.com" as the email address. Messages to that address come to my "Inbox". I don't use the address for anything else. I never send a message with that address. Years pass. I start receiving email solicitations for erectile dysfunction remedies and, oddly, woodworking plans (what is it with the spam for shed plans?) to that address. Either my address was sold or a data breach occurred. (It could have been my own data breached, but it seems unlikely, if that did happen, that the result would be me receiving spam only to that one specific address.)