subject encoding: What's =?ISO-8859-1?Q?

[Martin Bless]

I've started investigating how Barry Warsaw's 'mimelib' works.
(Version 0.2, http://mimelib.sourceforge.net/). Great, with mimelib I
can build mime-messages from scratch and the package offers a lot to
learn from. For example, the subject of the message can be set by
  msg.['subject'] = 'Greetings!'

However, if I create a message with Outlook Express (Windows) and the
subject has some german Umlaute ("Viele Grüße"), the subject looks
like this:
Subject: =?ISO-8859-1?Q?Viele_Gr=FC=DFe?=

(1) What kind of encoding is this? Hhm, especially the =?ISO-8859-1?Q?
part? Somewhere in the RFCs?

(2) And do we already have a function in the Python lib to generate
this encoding?

Martin