If you are using SpamAssassin then you need to update the rules now. There is a bug in the rules which will cause emails with a date of 2010 to be scored as spam. Here is an excerpt from the SA website :
Versions of the FH_DATE_PAST_20XX rule released with versions of Apache SpamAssassin 3.2.0 thru 3.2.5 will trigger on most mail with a Date header that includes the year 2010 or later. The rule will add a score of up to 3.6 towards the spam classification of all email. You should take corrective action immediately; there are two easy ways to correct the problem:
* If your system is configured to use sa-update run sa-update now. An update is available that will correct the rule. No further action is necessary (other than restarting spamd or any service that uses SpamAssassin directly).
* Add “score FH_DATE_PAST_20XX 0” without the quotes to the end of your local.cf file to disable the rule.
If you require help updating your rules to correct this issue you are encouraged to ask for assistance on the Apache SpamAssassin Users’ list. Users’ mailing list info is here.
On behalf of the Apache SpamAssassin project I apologize for this error and the grief it may have caused you.
Daryl C. W. O’Shea
VP, Apache SpamAssassin
If you do not want to update, a quick manual fix is to just edit your 72_active.cf and change:
header FH_DATE_PAST_20XX Date =~ /20[1-9][0-9]/ [if-unset: 2006]
header FH_DATE_PAST_20XX Date =~ /20[2-9][0-9]/ [if-unset: 2006]
Restart spamd and/or any other service that uses SA directly.
Source : WHT