Suspicious SMTP Submission Connection From Non-Mail Process

ATT&CK techniques

C2

Recon
Resource Dev
Initial Access
Execution
Persistence
Priv Esc
Defense Evasion
Cred Access
Discovery
Lateral Movement
Collection
C2
- T1071.001Web Protocols
Exfiltration
Impact

What it detects

This rule detects an outbound connection to TCP port 587 (SMTP submission) initiated by a process that is not a known mail client. This behavior matches .NET infostealers such as Agent Tesla and XLoader that were hidden in bitmap resources and exfiltrate stolen credentials directly over SMTP. Direct SMTP use by arbitrary binaries is a strong data-theft indicator.

Reporting behind it

Related detections9 linkedT1071.001 — drag to rearrange

Possible Remcos C2 Connection from eilowutil Process

Possible MOVEit Transfer SSRF via MOVEitISAPI action m2

Suspicious Tomcat Campaign Command and Control Domain Resolution (via dns_query)

Suspicious TeamTNT Command and Control Domain Resolution (via dns_query)

Malicious CastleLoader C2 Communication via Hardcoded User-Agent

Suspicious Outbound Connection From CasPol Binary

Suspicious Cobalt Strike Loader C2 Traffic via Forged MSIE yie9 User-Agent (via proxy)

GateDoor Command-and-Control via gateway REST Endpoints (via proxy)

PATCHCORD Beacon C2 Tasking via api.jsp clientId Poll (via proxy)

Suspicious SMTP Submission Connection From Non-Mail Process

Pivot detection · T1071.001 · 9 related

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.

Full detection rule

Unlock this rule to view and copy it

The detection logic is included with a plan. Everything else — context, mappings and implementation details — stays free on this page.

Sign in for 3 free unlocks

Signing in gives you 3 unlocks to spend on any rule in the library. No card, and they do not expire.

Also included

Unlocked rules convert on this page — to Splunk SPL or Splunk — Raw Index SPL or Microsoft Sentinel KQL or Microsoft Sentinel ASIM ASIM KQL or Microsoft Defender XDR KQL or Elastic Security KQL or Elastic Security Lucene or Elastic Security ES|QL or CrowdStrike Falcon CQL or SentinelOne PowerQuery or Palo Alto Cortex XDR XQL or Carbon Black Cloud Platform Search or Carbon Black EDR Process Search or Google Security Operations UDM Search or IBM QRadar AQL or Sumo Logic Cloud SIEM Rules expression or Rapid7 InsightIDR LEQL or Graylog Search or OpenSearch Lucene or OpenSearch PPL PPL or Grafana Loki LogQL or SQLite SQL or Zircolite SQLite — with the log-source profile the engine picked, the field map it used, and everything it could not express. Converting a rule you have unlocked costs no further credit.

See it run on a free rule →Convert your own rule →