Not sure I follow. Are you saying that a substantial number of people is routinely using your _fastmail_ address with services that send _marketing_ emails to

Not sure I follow. Are you saying that a substantial number of people is routinely using your _fastmail_ address with services that send _marketing_ emails to _unverified_ email addresses? I find this highly implausible. Edit - Why the downvotes? If I read the OP correctly, they have such a common address that random people mindlessly type it into various subscription nags. Can you think of a such @fastmail address? If it's not that common, then their address was just leaked and ended up on the spammers list, so tagging as spam is a proper thing to do. However it sounds like the OP also spam-tags bulk emails they don't like even if they are subscribed to those, which is as ass thing to do. It hinders delivery to others, nicks the sender reputation, etc.