SpamAssassin 2010 Bug
SEWilco writes "You might want to check your spam folder, as SpamAssassin has a rule which is tending to mark email sent in 2010 as spam. There is some discussion in a bug report. The SpamAssassin Wiki FH_DATE_PAST_20XX page doesn't have discussion, but it was updated today with a different date rule."
Exactly. This is the right "fix" right now - the bug is out there causing real problems, and the fix (while definitely a filthy hack) is well-understood and can be pushed out immediately. If the same thing were to happen ten years from now (or the threshold quietly got pushed back to 2030), that would be nothing short of negligent.
Your solution doesn't work.
It fails on new years eve if someone is in a different time zone or if their clock is slightly off.
I'd suggest that any message sent more than seven (pick your favorite number) days in the future is spam.