SMTP to the Internetedit

Detects events that may describe SMTP traffic from internal hosts to a host across the Internet. In an enterprise network, there is typically a dedicated internal host that performs this function. It is also frequently abused by threat actors for command and control, or data exfiltration.

Rule type: query

Rule indices:

  • filebeat-*

Severity: low

Risk score: 21

Runs every: 5 minutes

Searches indices from: now-6m (Date Math format, see also Additional look-back time)

Maximum signals per execution: 100


  • Elastic
  • Network

Version: 3 (version history)

Added (Elastic Stack release): 7.6.0

Last modified (Elastic Stack release): 7.7.0

Potential false positivesedit

NATed servers that process email traffic may false and should be excluded from this rule as this is expected behavior for them. Consumer and personal devices may send email traffic to remote Internet destinations. In this case, such devices or networks can be excluded from this rule if this is expected behavior.

Rule queryedit

network.transport:tcp and destination.port:(25 or 465 or 587) and
source.ip:( or or and not
destination.ip:( or or or or "::1")

Threat mappingedit


Rule version historyedit

Version 3 (7.7.0 release)

Updated query, changed from:

network.transport: tcp and destination.port: (25 or 465 or 587) and (
network.direction: outbound or ( source.ip: ( or or and not destination.ip: (
or or ) )
Version 2 (7.6.1 release)
  • Removed auditbeat-*, packetbeat-*, and winlogbeat-* from the rule indices.