I don't know the legal side of things, but in terms of the current protocol, the default fixed mixin count is the current implementation.
I.e., if you type
transfer gingeropolous@payxmr.com 500 1
it will send me 500 1 xmr with a mixin (or ring size) of 3.... and nowhere in the command is there a 3 specified.
Let me test that.
transfer gingeropolous@payxmr.com 1
For URL: gingeropolous@payxmr.com, WARNING: DNSSEC validation was unsuccessful, this address may not be correct!
Monero Address = 46aRPgXEgqf23G2VU5fy4oeKBGpU6uXSv57CkXKrz4EbDwDeh573QQhZYeyjriWAMUhNoBHMUwkGV2A2ppWwAx4JT9HNJ9h
Is this OK? (Y/n) y
Money successfully sent, transaction
Wow, how does that work (the sending to your 'email' part)? Pretty cool!
Edit, the default 'mixin' is 4 by the way (when / will we be changing that incorrect term?)
http://moneroblocks.info/search/aabb4052eec0b2097246c2bd4ff2d5421a1ffdb086bbe42d7318500db22280b4the magic of openalias, brought to you by the monero developers, even though it can be used by any cryptocurrency.
there are some services in the community to get your own alias, though you can do it yourself if you have your own domain name, or if you feel like using one of the available domains on afraid.org