I've been asked about shipping cupcakes in a jar overseas. I've also seen postings for people to make cupcakes in a jar and ship overseas. Here is why I don't unless it can arrive and be eaten within 5 days... I don't use preservatives. Box and other mixes and pre-made frosting's contain a preservative that helps them last longer. That's why cakes in some stores on a shelf or their fridge can last a week or 2! Fresh, real buttercream frosting will last up to 4 days on a regular cake or cupcakes. Out of a jar, cakes and cupcakes will last 2 days nicely. It's the jar that helps keep the cake and frosting fresh a few days longer. I won't eat anything past the 3rd day and if I wouldn't I wouldn't want others to.
I personally don't feel comfortable shipping cupcakes in a jar that would go past an expiration date and put the other person at risk. I'm just that way. To ship these cupcakes or cakes, I would need to add a preservative and I'm not keen on preservatives unless its a natural preservative. So I'm still researching this because I would like to be able to ship cakes and jar cupcakes to soldiers deployed.
The cupcakes in a jar do freeze nicely though. I can't eat a dozen cupcakes within a few days so what I do is make cupcakes in a jar for myself and then freeze them. I take one out about 2-3 hours before dinner and its thawed and ready to eat. No waste and its an individual portion. They freeze well for up to a month. I'm always open to suggestions about shipping cakes overseas. Just my thoughts, experience and opinions.