Well no the lowest fee is 0 BTC (for high priority transactions). Only low priority transaction have a mandatory fee as a denial of service prevention mechanism. All tx fee (both mandatory or optional) go to miners.
Excuse my sounding like a newb, but this escaped me. What are low/high priority tx?
It is calculated by a combination of transaction size, transaction value, and input age. Smaller transactions with old coins will be high priority. Larger transactions with new coins will be low priority and will require a fee.
https://en.bitcoin.it/wiki/Transaction_fees#Technical_info
Quote
priority = sum(input_value_in_base_units * input_age)/size_in_bytes
Likely a typo in there (smaller and larger mixed up).
I meant smaller/larger size_in_bytes, but I'll clarify it.
@molecular. A general rule of thumb (because nobody except the client is going to use the formula) is "one bitcoin day". If your inputs are "one bitcoin day" or greater then your tx is high priority and no mandatory fee is required. You may still wish to include an optional fee to faster processing but the tx will be relayed by all nodes as having sufficient priority for no fee.
The actual threshold is one bitcoin day per 250 Bytes. So your rule of thumb works as long as the total transaction doesn't have too many inputs/outputs.
