$ perl -Mutf8 -MEncode -E 'say encode("MIME-Header", "Hallöle")'                                                                      
=?UTF-8?B?SGFsbMO2bGU=?=
$ perl -MEncode -E 'say encode("UTF-8", decode("MIME-Header", "=?UTF-8?B?SGFsbMO2bGU=?="))'                                    
Hallöle