Do you run SpamAssassin to remove spam from your mailbox? Have you noticed a fall in the amount of mail you've received in the last couple of days? I mean all mail, not just spam.
You might well be falling foul of this problem. The rules in the latest version of SpamAssassin available from CPAN include this rule.
header FH_DATE_PAST_20XX Date =~ /20[1-9][0-9]/ [if-unset: 2006] describe FH_DATE_PAST_20XX The date is grossly in the future. ##} FH_DATE_PAST_20XX
And here are the scores for that rule:
score FH_DATE_PAST_20XX 2.075 3.384 3.554 3.188 # n=2
Basically, any mail with a date header greater than 2009 is given a score of about 3. Depending on your local configuration and other rules that the mail might trigger, that might well increase the chance of legitimate mail being marked as spam.
So have a look in your spam folder. You might find some good stuff in there.
Of course, I might be the only person who has been caught by this. It's possible that you all knew of the existence of sa-update and you've all got it running in a cronjob so you're using the latest rules and not the eighteen month old set that I have. I'll be setting that up today.
This has been a public service announcement for people who are as stupid as me.