You can store the email addresses in a database for each of the different categories and then create a recordset that will return the email addresses for that category. When creating the Universal Email Server Behavior, in the TO: tab of the wizard, select the Recordset Loop option and you will be able to send out the emails to each of the users in the database that way.
It is not recommended to send out a large amount of emails this way however, since it takes up a lot of resources on the server, the server may block you thinking that you're a spammer or you may block out other services while sending out the emails. There are mailing services that are built specifically for this kind of mailing list if the list gets very large.