Dee, anything that needs to be refrigerated should not be sent via mail. Cream can spoil and butter can go rancid. You also have to consider the climate you are mailing to--if humid, toffees, caramels, buttercrunch can become sticky--if too hot, chocolates can melt.
If you must, go to a local chocolate shop and ask them how they ship--do they use a cold pack, styrofoam and overnight?
My biggest concern usually has to do with not making people ill--so if something can spoil, I don't risk it and mail it.
Things like rum and bourbon balls mail well but often need to be redredged in sifted powdered sugar before serving, unless your friends aren't picky.