RFC8222 парсер для CL или Scheme

... RFC2822, разумеется ...

http://common-lisp.net/project/rfc2822/

Насчет "полнофункциональный" не знаю, разбирайся сам.

Нет, скорее всего пионерская поделка: "my initial regex-based approach will not cut it. I'll have to write a proper specialized parser. Since I don't know how to do that, I'm currently reading books on how to do it."

:))