For some weird reason, all my inbox email in the Mail app and all the birthdays in my Address Book entries are set to the 5th of each month. All the emails I received in the month of January, for example, reflect 5 January 07. This applies to all the past months. My friend's birthday in Address Book, which is on 12 Feb, says 5 Feb! Clicking on EDIT in Address Book reveals the CORRECT bday info, but when I save it, it says the 5th pa rin! Anyone else experiencing this behavior?
You have to troubleshoot on the settings of your mail as well as the addressbook. What is your OS? How many account do you have on your mail?