Suspicious Outbound SMTP Connections
Adversaries may steal data by exfiltrating it over an un-encrypted network protocol other than that of the existing command and control channel. The data may also be sent to an alternate network location from the main command and control server. This rule detects suspicious outbound SMTP connections by looking for connections to common SMTP ports (25, 587, 465, 2525) from processes that are not common mail client applications like Thunderbird or Outlook, or Microsoft Exchange Server processes.
Sigma
