From Bitcoin 0.8.2 release notes
https://bitcointalk.org/index.php?topic=219504.0Payments (transaction outputs) of 0.543 times the minimum relay fee
(0.00005430 BTC) are now considered 'non-standard'
I've read a lot about transaction fee, and i think i've wrapped my mind around it.
What's relay fee ? Is it different from transaction fee ?
The transaction fee is a voluntary payment.
However, there are various limitations built into various common functionality. If you don't pay an appropriate transaction fee, you can encounter problems with some of these limitations.
Under some circumstances, the Bitcoin Core wallet won't broadcast its own transaction unless it has a large enough fee. This could be referred to as a minimum broadcast fee.
Under some circumstances, peer nodes running code based on BitcoinCore won't relay a transaction unless it has a large enough fee. This could be referred to as a minimum relay fee.
Under some circumstances, some mining pools won't confirm a transaction unless it has a large enough fee. This could be referred to as a minimum confirmation fee.
The point is, they are all just ways of talking about a minimum fee that a transaction must include if it is going to make it past a particular limitation.
If your wallet won't broadcast the transaction, then nobody will ever know about it.
If your peers won't relay your transaction, then your recipient might not see the transaction until it is confirmed, and it might not be confirmed for a very long time since many miners (and mining pools) won't hear about it from their peers.
If many of the miners (and mining pools) won't confirm it, then it may remain with 0 confirmations for a very long time. Depending on the wallet you are using, the transaction may expire if it isn't confirmed, and the bitcoins could end up back in your wallet.
