Bitcoin Forum

I thought, that comission is not mandatory.
But right now Bitcoin QT would not allow to send 0.02 - 0.2 BTC without 0.0005 comission.
Is that supposed to be this way?
Thank you.

There is a "mandatory" fee in certain instances, to have your transaction included in a block. The QT client forces you to include a fee/bid/commission/whatever-you-want-to-call-it in those instances because to not do so would possibly cause your transaction to either never be processed, or take an exceptionally long time.

There's a fairly complete explanation here:
https://en.bitcoin.it/wiki/Transaction_fees

The fee structure has changed a few times, and there are a ton of variables involved in whether or not you could reduce or eliminate the fee in a non-QT client (since peers and miners' choices in settings also affect which transactions get through). It's generally a good idea to pay whatever QT wants, though, since it assumes everyone's using default inclusion/relay settings with regards to fees (I suspect the vast majority of peers and miners are using default settings).

Thanks.