- Management Consultants & Services, Dover
- Manufacturing, Dover
- Marble, Dover
- Marinas & Marina Services, Dover
- Marriage & Family Counselors, Dover
- Masonry Materials & Supplies, Dover
- Medical & Health Service Organizations, Dover
- Methodist Church, Dover
- Mexican Restaurants, Dover
- Mini & Self Storage, Dover
- Miscellaneous Business Services, Dover
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- Miscellaneous Government, Dover
- Miscellaneous Industry, Dover
- Miscellaneous Personal Services, Dover
- Miscellaneous Photographers, Dover
- Miscellaneous Professional, Dover
- Moldings Materials, Dover
- Mortgage Bankers & Correspondents, Dover
- Motor Vehicle, Dover
- Motor Vehicle Rental & Leasing, Dover
- Moving Truck Rental , Dover
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