alert tcp $EXTERNAL_NET any -> $HOME_NET 25 (msg:"ET DELETED Possible Image Spam Inbound (3)"; flow:established,to_server; content:"Content-Transfer-Encoding|3A|"; content:"R0lGODlh"; depth:575; content:"AOAgAABAACBAAEBAAGBAAIBAAKBAAMBAAOBAAABgACBgAEBgAGBgAIBgAKBgAMBgAOBgAACAACCA"; content:"AECAAGCAAICAAKCAAMCAAOCAAACgACCgAECgAGCgAICgAKCgAMCgAOCgAADAACDAAEDAAGDAAIDA"; classtype:misc-activity; sid:2003120; rev:4; metadata:created_at 2010_07_30, signature_severity Unknown, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2019_07_26;)