X-Message-Info

Mysterious headers appearing in spam recently:

    X-Message-Info: 0oROdu983rDK/jdJaczEMfHXwmauX6Wf

Turns out spammers think that this gets them past Hotmail's filters

because a Hotmail message saved to disk contains this header?

Result: X_MESSAGE_INFO SpamAssassin rule hits 37% of spam, 0.0004% ham