Last year we had a mass mailout to all our clients to wish them Merry Christmas. I need to categorise this list of contacts included in the mailout under the heading 'XMAS 2012' and then work on it to create XMAS 2013.

The list of email addresses has been retrieved from the sent mail and it is too time consuming for me to search for each contact individually and apply the category. I have already applied the contact to 400+ contacts and it has taken too much time already.

Would appreciate all the suggestions I can get.