Are you implying that plus addresses are part of RFC 2822? Because they aren’t. AFAIK, no RFC documents specify the plus address convention. The RFCs merely specify that, in an email address, whatever is to the left of the @ sign is to be interpreted by the receiving system, and nobody else should make any assumptions about any of it, and certainly never alter it. And also that the + character is one of the many permitted characters to the left of the @ sign in an email address.
The plus address convention is just that, a convention, widely implemented by many email programs and servers, but not required by any standard, nor universally implemented.
“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.
The normalised version is what gets redirected to trash, according to GP's proposal. Legitimate senders who do not normalise have their mail delivered to the inbox.
It's become a fairly regular occurrence that any email with + just shows an error saying the email isn't valid. Bad actors can also easily strip it out after
The plus address convention is just that, a convention, widely implemented by many email programs and servers, but not required by any standard, nor universally implemented.