When creating tasks via e-mail you may have a question about how to indicate the due date to make it understandable for the system. The best way is to write it in this format:
Nevertheless Wrike supports another format: [mm-dd-yyyy]. You may separate the year, month and day with the help of any of following symbols: . - /.
So if you really like, you can type something like the following: [yyyy/mm/dd].
Update: Wrike now supports the international date format where the day goes first and the month goes second, like 31/12/2008.