Hmmm... I'm not sure. This code works for me, with the header value from your original post. 
use Encode;
my $header = '=?UTF8?B?5LuO5Y2a5a6i5paH56ug5Lit5p+l5om+5oKo5oSf5YW06La
+j55qE5Li7?==?UTF-8?B?6aKY?=';
my $utf8   = decode('MIME-Header', $header);
print "uft8: $utf8\n";

[download]
output is:
uft8: 从博客文章中查找您感兴趣的主题

Of course, I can't read any Chinese, so I have no idea if those are the right characters or just gibberish.

In reply to Re^3: Mime::Parser utf-8 issue by blahblahblah
in thread Mime::Parser utf-8 issue by mhearse

Title:
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and:  <code> code here </code>
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