Can different clients have different transaction fees? BitCoin Wiki states:


  Different bitcoin clients and different versions have different rules for determining which transactions to accept and how large a fee to send..


Is it true that different clients can attach different transaction fees which differ from the other clients?

For example, is there anyway to send 1 mBTC without having to pay the fee of 0.5 mBTC?

Are the rules of the transaction fees enforced by the protocol?
The Bitcoin protocol does not require any fee to be paid.

However, the standard client will require varying fees to be paid before the transaction is included in a block or relayed, all depending on the current load (up to 27kB transactions are free unless they are considered spammy, then fees get higher and higher).

Some pools (like Eligius) don't include transactions without fees into their blocks, so that's another incentive to pay something.