No, it is not necessary to vent a microwave oven outside. Unlike range hoods or exhaust fans used in kitchens, microwave ovens do not produce combustion byproducts that need to be vented outside.
Microwave ovens use electromagnetic waves to generate heat and cook food, so they do not produce smoke, fumes, or odors that require external ventilation. The main purpose of the built-in venting system in a microwave oven is to remove excess steam and moisture that can accumulate during cooking, helping to prevent condensation and keep the cooking area dry. This ventilation is typically achieved through a vent located at the top or rear of the microwave oven.
However, it is important to ensure that the vent is not blocked or obstructed to allow proper airflow and prevent any potential overheating of the microwave. It's also a good idea to follow the manufacturer's instructions regarding the installation and use of the venting system in your specific microwave oven model.