What I've done for years: "generate" email addresses on the fly like zz-<portal>@mydomain.com and have a catchall rule for zz* in my main inbox. So if I get any mail or spam I can see where it originates from (and by doing this it I was able to point a portal to the fact that obviously they leaked mail addresses). By doing this I can block a single mail address.
This does break though when you are required to SEND with this email address.
This does break though when you are required to SEND with this email address.