Will TSA approve a brand New bottle of perfume still in the box never opened in carry on luggage? 3.4 oz/100ml
First, Whether or not something is new, opened, in the box etc is irrelevant to TSA. Customs may have an opinion, but not TSA.
Second, 100 ml is small enough for carryon, though you might be asked to put it in the freedom baggie. The box, if it is very large and decorative, might prevent you putting the perfume in the freedom baggie. If this happens they will probably ask you to open it.
If it is important to you that it stays in the box unopened (perhaps it's a gift) then packing it in your checked luggage is a better plan. There is no specific limit on the amount of liquid you can have in checked luggage: large bottles of shampoo, bottles of wine and so on are all ok in checked luggage.
Brand new or not, you must put it in the baggie. If it's 3.4oz it is within guidelines. Check the liquids rule.
You are allowed to bring a quart-sized bag of liquids, aerosols, gels, creams and pastes in your carry-on bag and through the checkpoint. These are limited to 3.4 ounces (100 milliliters) or less per item. Placing these items in the small bag separate from your carry-on baggage facilitates the screening process.
The only exception is if
- You are traveling internationally to the United States with a connecting flight.
- They are in transparent containers.
- You bought them at a duty-free shop where it is packed in a secure, tamper-evident bag.
My experience with the TSA shows that it almost doesn't matter how much liquid you have as long as the label on the bottle will say that it is 100ml or less. If there is no label, they have no way of gauging it. Therefore, make sure that it is visible on the package.
It also has to fit (box included) in the "freedom" bag, of course. If it doesn't, well... check it or mail it.