UTF-8 Subject line appears as question marks in Gmail

I am trying to send an email with Chinese characters in the subject line from my program to a gmail account, but the subject line appears as ??开发者_运维知识库??. This is how the subject line is encoded:

=?utf-8?B?Rlc6IOiri+W5q+aIkee1piDoiIfkvaDotbfkvobnmoTlkIzkuos=?=

Is there anything wrong in the encoding? Is there anything that I have to bear in mind? The mail also contains Chinese characters in the body, but those get displayed just fine. I am using base64 to encode the body.

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=?utf-8?B?Rlc6IOiri+W5q+aIkee1piDoiIfkvaDotbfkvobnmoTlkIzkuos=?= is encoded by base64, and the string-buffer(after decoded by base64) is encoded by utf-8.

You can decode it in python:

>>> from base64 import b64decode
>>> b64decode(b'Rlc6IOiri+W5q+aIkee1piDoiIfkvaDotbfkvobnmoTlkIzkuos=').decode('utf-8')
'FW: 請幫我給 與你起來的同事'

Also in python:

>>> from email.header import decode_header
>>> decode_header('=?utf-8?B?Rlc6IOiri+W5q+aIkee1piDoiIfkvaDotbfkvobnmoTlkIzkuos=?=')
[(b'FW: \xe8\xab\x8b\xe5\xb9\xab\xe6\x88\x91\xe7\xb5\xa6 \xe8\x88\x87\xe4\xbd\xa0\xe8\xb5\xb7\xe4\xbe\x86\xe7\x9a\x84\xe5\x90\x8c\xe4\xba\x8b', 'utf-8')]
>>> _[0][0].decode(_[0][1])
'FW: 請幫我給 與你起來的同事'

Or in bash(maybe you should pipe to iconv):

~ $ echo Rlc6IOiri+W5q+aIkee1piDoiIfkvaDotbfkvobnmoTlkIzkuos= | base64 -d
FW: 請幫我給 與你起來的同事

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For those interested in the answer to this question, this string is a MIME header encoded as per RFC2047. =?utf-8?B?Rlc6IOiri+W5q+aIkee1piDoiIfkvaDotbfkvobnmoTlkIzkuos=?= means it uses the UTF-8 charset, B means Base 64 encoding.

In PHP, use iconv_mime_decode.