[teddyh]

“Talked about” is exactly correct. That RFC describes it as an existing practice and describes one common use where the + sign is used. Which is correct. But this is all completely independent of the email protocols and the RFCs which define them. This specific RFC is about how to handle email filtering where you want to take such an extra “detail” string into account, if such a string is present and can be parsed out of an email message, once it has been recieved. Note that this RFC does not describe the + sign convention as the only one – it shows two other possible syntaxes.