How do you send betta fish via mail?

First of all, if you're in a temperate country shipping is going to be very tricky in the colder months, and never ship more than a few hours away - especially not internationally!

I would recommend looking into poly boxes and heat packs, these are how Bettas are shipped, together with plenty of packing to stop them getting bashed about. Contact other breeders through http://www.ibcbettas.org/ or other such site and they can run you through their methods, everyone has their own little trick.

Lastly, you can't send them by regular mail!! Courier only! And you'll have to look into couriers that are willing to take live animals - many won't! Some breeders skirt round this by stating the Bettas are live food instead!

If you are wanting to do that your probably better off finding a local or a few local aquarium/pet shops in your area to offload them to. They would be more than happy to take them off your hands and saves your time and effort trying to post them

bad idea... mail? as in post mail... :O