While what is stated above is true... there are some other points here.

It is hard to have a typo in an address (from what I read somewhere).  If you send to an invalid address, the transaction just fails.

If you mix up your clipboard and send to the wrong, yet valid, address... then you have no recourse as there is no way to get the coins back unless a person holding the private key to that address sends them back to you.

I once overpaid someone using mybitcion... and they were kind enough to give me the extra, so if you can find out who the coins went to, there is a chance.