What kind of fee is this "minrelaytxfee"?
Why did I always allow you to always send for 1 Satoshi\byte, since what day are such innovations on the bitcoin network now?
The minrelaytxfee option has been around since at least 2013, but even before then there was a minimum fee required to broadcast low value transactions.
Initially, any transaction creating an output of less than 0.01 BTC was required to pay a fee of 0.0005 BTC per every 1000 bytes of transaction data (rounded up). This was decreased from 0.0005 BTC to 0.0001 BTC in Bitcoin-Qt 0.8.2, and then to 0.00001 BTC (1000 sats) in Bitcoin Core 0.9.0. This is the same level it sits today, at 1000 sats per kilobyte, or 1 sat/byte.