As far as I understand, if I don't want to pay any fees, I have that option.
1. Am I right assumming this?
Bitcoin is a voluntary system. It is not "required" that you include a fee. You are welcome to attempt to broadcast a transaction with no fee (some wallets prevent this under certain circumstances, others will allow you to do so regardless of the circumstances).
However, peers are not "required" to relay your transaction. They are welcome to refuse to relay it for any reason they like. Most peers will be running the "reference client" called Bitcoin-Qt. In that case they will relay most all transactions, but if the transaction appears "spammy" or like it could potentially be part of a denial-of-service attack on the network, then they may refuse to relay the transaction if it doesn't include a sufficient fee.
Additionally, miners are not "required" to include your transaction in a block. They are welcome to refuse to include it if they feel they can increase their profits by including some other transaction that has a fee instead of your "free" transaction.
This all being said, most all "free" transactions where all outputs are greater than 0.01 BTC and the total size of the transaction is less than 10 kilobytes, will be relayed and will eventually be included in a block by a miner. Miners see a long term benefit to maintaining a system that is cheap and easy to use. The miners are currently subsidized by the minting of new bitcoins, and they get enough revenue from that subsidy that they are generally willing to include a reasonable number of "free" transactions in each block they mine.
Note that if any one or more of the following are true the transaction may not be relayed by most peers and may not be included in a block by most miners:
- The transaction is larger than 10 kilobytes
- Any one or more outputs of the transaction are less then 0.01 BTC
- The transaction is considered "low priority"
Priority is determined by the following formula:
priority = sum(input_value_in_base_units * input_age)/size_in_bytes
where base units is Satoshis, and input age is number of confirmations on the input. Any priority less than or equal to 57,600,000 is considered "low priority".
2. I cant seems to force blockchaif.info to make a transactions without fees. Why?
Because blockchain.info is a wallet that enforces fees under some situations. You can create a raw transaction and transmit it using the transaction tab at brainwallet.com if you like, but if blockchain.info is refusing to create the transaction without a fee you'll probably find that miners will refuse to confirm it for you as well.
