See also the following functions which may work better in some cases:
iconv_mime_decode() - http://php.net/manual/function.iconv-mime-decode.php
imap_utf8() - http://php.net/manual/function.imap-utf8.php
(PHP 4 >= 4.0.6, PHP 5, PHP 7)
mb_decode_mimeheader — 解码 MIME 头字段中的字符串
$str
) : string
解码 MIME 头中编码过的字符串 str。
以内部（internal）字符编码解码的 string。
See also the following functions which may work better in some cases:
iconv_mime_decode() - http://php.net/manual/function.iconv-mime-decode.php
imap_utf8() - http://php.net/manual/function.imap-utf8.php
This function ignores any encoded-word specified in a character set not supported by the mbstring extension (e.g. Arabic windows-1256). Such encoded-words pass straight through.
RFC2047 doesn't specify the behaviour, but common agents such as Gmail, Windows Mail, etc. DO NOT ignore such encoded words. They are decoded as if they were declared to be in the local character set.
Be aware of this idiosyncrasy.
Using quoted-printable-encoding the hex-numbers must be written in uppercase letters!
Works: =?iso-8859-1?q?=3F=3F=3F?=
Fails: =?iso-8859-1?q?=3f=3f=3f?=