Go to File, select Export.
Export to a File (CSV - either DOS or Windows is generally preferred)
Select your contact list to export.
Tell it where you want to save (Desktop)
Import data, point it at the CSV file, go through the wizard.
Voila. Delete the columns you don't want.
Find the column with catagories.
Sort all Rows/Columns off that column.
Now that they are all together, select the range that has their SMTP address. COpy.
Open Outlook, new message.
Paste in the BCC field. (If you don't want everyone having everyone elses email address). Otherwise put it in To.