Furikomi only in that bank?

Well, I have a post bank account, but only with a normal ATM card (no credit-card).
I am buying a lot on Yahoo and when sending money I always go to the bank in which account I am sending money to was made (or its ATM). Do I really need to do it? Can't I just go to any bank I'll see and send it from there? There so many options and sometimes it takes ages to find the right one...

Have you tried online banking? You can transfer money from a Post Office account to other banks. I have tried this online but I don't know if it is possible with ATMs.

Well, I have a post bank account, but only with a normal ATM card (no credit-card).
I am buying a lot on Yahoo and when sending money I always go to the bank in which account I am sending money to was made (or its ATM). Do I really need to do it? Can't I just go to any bank I'll see and send it from there?

You can send furikomi using your postal atm card at any branch of the Postal Bank (i.e. at any post office with an atm), but you can't do it at the atms of non postal banks.

If you are doing lots of yahoo auctions I'd suggest applying for a postal credit card, which would allow you to set up their easy pay online payment system that is used by many yahoo sellers. It allows online payment at a small fee, which is cheaper than atm furikomi fees when sending to non-postal accounts.