alert tcp !$SMTP_SERVERS any -> !$HOME_NET 587 (msg:"ET POLICY Outbound SMTP on port 587"; flow:established; content:"mail from|3a|"; nocase; threshold:type limit, track by_src, count 1, seconds 60; classtype:misc-activity; sid:2003864; rev:6; metadata:created_at 2010_07_30, confidence High, signature_severity Informational, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2019_07_26;)