If I received such an email I wouldn't do anything about it. 99.9% of the traffic we see from M247 is malicious and there is no chance that I would unblock this ASN on an online shop.
And that's fine! That's the beauty of the freedom of choice. I can take my business elsewhere and the company that banned the mullvad IP can have one less potential (but not really a) hacker to worry about.
