Thanks.
Free transactions have a minimum priority that dictates relatively large BTC amounts or well-aged coins. People can't continuously spam with this rule because they will quickly run out of funds that can be sent for free.
I know this is true for mining, i.e. CreateNewBlock, but my question is specifically about relaying/admitting to mempool. From what I can see, no matter how high the tx priority is, if there is zero fee then it's subject to rate-limiting. This suggests that even high priority transactions may not get relayed properly if they don't include a fee. Just want to make sure that I'm interpreting it correctly.