How do I export Outlook for mac contacts into excel and retain the categories for each contact?

I recently bought outlook for mac and spent a lot of time organising my contacts and categorising them.  I planed to use an email marketing campaign manager to send html emails but need to upload my contact.  In outlook for mac I exported the file as a tab delimited txt but when I opened it in excel all of the cells in the categories column are populated with "gb".  I've exported it several times but I can't figure out what I am doing wrong.  Please help as I've spent so much time organising my contacts in outlook and can't bear the thought of redoing it or manually entering the contacts in the excel sheet.