How to browse:

Requests for Comments, total over 8000 of them. I haven't see them listed as tree structure, seems all flat, not easy to browse. 

Some points:

Not all are from IETF stream. They don't change. When change needed, a new RFC is created, as update 

About emaill RFCs, as an example:

when I search SMTP on rfc.fyi , about 50 were found, mostly Informational or Legacy Here are some sample ones: 	SMTP to transport the email: RFC 5321, e.g. "RCPT TO" 	Email message format: RFC 5322 , e.g. "Subject:" 	Authentication SASL: RFC 4954 

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