Mac OSX server uses SpamAssassin to filter inbound spam for mail services. SpamAssissin increases the score on legitimate 2010 messages resulting in the messages being marked as spam. Apple has two resolutions, the first is to disable the date rule by editing "/etc/mail/spamassassin/local.cf". Apple's support document uses vi, I like nano so you can replace the sudo vi with sudo nano <fileName> or set the EDITOR value in your .profile file.
The second solution is change the date rule for scoring on future dates by doing the following.
Many administrator customize the SpamAssassin settings so any other date related flags must be checked. The change in the decade has resulted in several decade based bugs in various sofware packages on multiple platforms.