AddressHeader problem when FriendlyName is improperly quoted and contains comma

Bug report

Bug description:

Given an address text of the form: John Smith, Jr <johnsmith@example.com>
Because of the unquoted comma, the text is parsed as two addresses:
"John" <@smith>, "Jr" <johnsmith@example.com>
This is of greatest concern if the object is supposed to be a SingleAddressHeader.

I have also encountered TO and CC strings that have incomplete address specifications, containing only a Friendly Name. For these messages, I am only interested in the valid addresses, although others may want the existing behavior.

To work around both the parsing problem and the invalid address terms, I created a sub-class which discards any address where username or domain are not strings. My workaround does not correct for the incomplete Friendly Name, but it ensures a correct count of valid addresses. It would be desirable to implement a trap for unquoted commas, but there are so many challenges to parsing address lists correctly, I wonder if fixing the unquoted comma problem will create other headaches.

Problem observed on Python 3.11.3150.0 and Python 3.8.1

CPython versions tested on:

3.11

Operating systems tested on:

Windows

從 CPython 的 AddressHeader 解析行為著手，並在回報中涉及的 Python 版本上重現未加引號的逗號和不完整地址項目的範例。在決定預期處理方式之前，先檢視留言中的討論；只有在針對無效或解析有歧義的地址項目達成一致的處理行為後，才算完成。