Then, the MIME text/plain part contains this text: "Your mailer do not support HTML messages. Switch to a better mailer."
I am not a native English speaker, but I feel the sentence is not correct and a bit offensive. Is any real email client actually using it? Or I can write a nice rule to contribute blocking this kind of spam?
No, the sentence is is not correct. It SHOULD say "You are smart enough to disable HTML Please turn it on so my webbig and tracking image will confirm your e-mail address is valid. And switch to a Microsoft e-mail client while you're at it too."
