I'm surprised your sniffer hasn't fallen right off from the powerful stench of these emails. There are variations in text, like "your account is closed", variations on the "your system administrator" theme, and in the earlier incarnations, "message couldn't be encoded, attached instead". It's all the delivery mechanism for a virus, usually MyDoom. The common semantic theme is text that urges you to open an attachment, thereby infecting your computer. Learning to recognize the message, however worded, is a powerful defense.

[Wagging finger in your face self-righteously] Geez, Bowser, the fact that this is even an issue tells me you probably don't have anti-virus software, or it's out of date. For god's sake, dawg, put some protection on your little computer! If not for yourself, then for the sake of everyone who has had or ever will have email relations with you. Remember, on the Internet, everybody you've ever had contact with therefore has contact with everybody else, through you. Don't be a virus vector!

(This message brought to you by the President's Council on Cybernetic Fitness and Online Moral Purity, a division of the Ministry of Fatherland Security. Remember our motto: "If you don't watch out, we'll watch out for you!")