超文本格式的垃圾邮件如果过滤?
最近经常受到一些反动言论的垃圾邮件,是超本本格式,发送人都是采用常用的sina、163、21cn等免费邮箱,邮件头的信息也无正常,主题一般与地震有关,但是加入许多特殊符号,无规律可循。在非超文本格式下,内容是乱码,比如为:MWlDeDVMT0ZXTDlhR3RmNFhoMmhvbTZ6UDJqc0ZtN3h0elNvOHVTVTZQU0E2WHNVNWxaaHhU
RmFNT3RoMW9Da01peUtEZXR4VWJYUQpaZnlTcW9YTDdzS0o3MVBXZmY2Um9zcVB2SmNmSVhU
djBpZGZ3Wk9yaG8xY2RHV2pKUVlYN2VDc0xDeGtwZUZlbUhqR3dYWUJhUENkCmpva1M1OUUy
YjRpTnhEWEtIcU9VWFZxaEhjSkZSOUdZblJGZ085NlAzZXNvSGRYZnV6WGhsYnBRZVdsVFZS
STZ3ZGRhYTdRMWM2Z0gKYTFNdXF4enp6T2ZCeW9rajRTZ3FUaHJUZTVMZzFQT1pHb2pXS0ht
N2pweUlFSVJ5cFZNNjIzUTdXcGJNMk5CeTBKaUFnc3hwR1ZYYQpyRHdHbzhEZjBoYU11Ym1t
UE9JRmxRM3I3b0VEN3FCb1RYVDVUa2FKcGFrSmF1VFA4cmloNTl3Mm4xdGtoVXdZRmZUcG5T
V0NRNGJRCnBVdGw5enQ1eVBYSkVmVExaZ3p2amhJeFhzWkRuWmlBSHpMSFgyQ2pHblRhc0FN
Z0U5ek1lNTkxbld0eUx6WWhXQU9KcWVSV3J5WEkKV3hPcndkMXo4WXFqS0hJazZ3?请问该如何过滤?(灰名单已经开启了)