Update selected RFC 2822 references to RFC 5322

[filiplajszczak]

Documentation

There are multiple references to RFC 2822 in documentation, docstrings and comments. Some of these should be updated to RFC 5322 (that obsoleted RFC 2822), and it looks like some should be kept as they are because they belong to the legacy email API. In some cases the reference to both RFCs should be kept to explain the evolution of the standard.

Linked PRs

• gh-139434: Update selected RFC 2822 references to RFC 5322 #139435

[AA-Turner]

It would be useful if you would conduct a survey and suggest places that could be updated. We would need to be careful of compatibility concerns, though, especially if we claim conformance to the new RFC.

A

[filiplajszczak]

5322 was mostly clarification and cleanup of 2822 (and it happened in 2008). Structure and big part of wording was preserved. 5322 compliance is already claimed in the top email docs. Looks like all the claims where update is proposed are still valid.