What do these '=?utf-8?' sequences mean in python?

[Dieter Maurer]

Chris Green wrote at 2023-5-6 15:58 +0100:
>Chris Green <cl at isbd.net> wrote:
>> I'm having a real hard time trying to do anything to a string (?)
>> returned by mailbox.MaildirMessage.get().
>>
>What a twit I am :-)
>
>Strings are immutable, I have to do:-
>
>    newstring = oldstring.replace("_", " ")

The solution based on `email.Header` proposed by `jak` is better.