attachment name

I have received an email with a file attachment defined as follows

Content-Type: application/octet-stream;
        name="=_UTF-8_B_RWXLY3RYB25PYYBQYXLTZW50IC0GNZMXNI5WZG_23"
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
        filename="=_UTF-8_B_RWXLY3RYB25PYYBQYXLTZW50IC0GNZMXNI5WZG_23"
Content-ID: =_UTF-8_B_RWXLY3RYB25PYYBQYXLTZW50IC0GNZMXNI5WZG 23

At first I thought the file name could be decoded via base 64 because of the
UTF-8_B part but when I decode RWXLY3RYB25PYYBQYXLTZW50IC0GNZMXNI5WZG I get
nothing meaningful.  Any idea what is going on here?  Thanks