Derive them, do not invent them
Read a hundred recent enquiries and group them by what the customer wanted. The categories will emerge, and they will not match your org chart — which is the point.
Five to eight, not thirty
Too many categories means agents pick inconsistently and the data is noise. Too few means everything lands in “General” and the data is absent. Five to eight is the range where people classify accurately.
Ban the general category, or watch it
If “Other” exceeds about a tenth of volume, something real is hiding in it. Read thirty of them and you will usually find a missing category worth creating.
Name them the way customers think
Customers pick the category on the form. “Billing” works. “Revenue operations” does not, and every mis-picked category is a transfer somebody has to make.
Review quarterly
Volume shifts as your business changes. A category list set up two years ago is describing a business that no longer exists.