They should stop interaction, preserve the original evidence, and use the approved reporting path without attempting improvised cleanup. The goal is to avoid destroying forensic value or giving the attacker more time. If email or identity systems are affected, staff should switch to an alternate channel and follow the response plan rather than making independent remediation decisions.
Why suspicious messages should be treated as evidence, not as a cleanup task
When a message looks suspicious, the first priority is to preserve its forensic value. Deleting, forwarding to personal accounts, stripping headers, or trying to “fix” the message can remove the very clues the response team needs to understand scope, timing, and delivery path. Treat the message as an artefact to be reported, not a problem to be improvised away.
The practical decision is to stop interaction immediately and avoid any action that changes the original content or metadata. That includes replying, clicking links, opening attachments, or editing the message in place. If the organisation uses centralised reporting, the report should capture the original message intact so investigators can assess whether it is phishing, social engineering, malware delivery, or a broader compromise attempt.
What to preserve and what not to touch
Preservation means keeping the original message, its headers, and any attached files or embedded indicators in their unmodified form. Those elements help responders trace sender infrastructure, authentication results, redirect chains, and possible campaign overlap. If the platform supports it, preserve timestamps and message context as well, because those details can matter when the team is correlating reports across users or systems.
Do not attempt informal cleanup before containment is complete. Removing the message from inboxes, rewriting the text into a safer-looking version, or pasting its contents into chat can complicate chain of custody and obscure whether the message has already reached other users. The safest approach is to keep the original evidence available to the people who are responsible for triage and analysis.
How reporting should work while containment is still in progress
Use the approved reporting path and let the response process decide what happens next. In a mature workflow, the report routes to security operations, mail administrators, or incident response with enough context to investigate without requiring the recipient to make a judgment call about severity. If the message appears to involve an email account or identity system, switch to an alternate channel for coordination so the response is not blocked by a potentially affected account.
That same discipline applies when people feel pressure to act quickly. The recipient’s job is to preserve evidence and escalate; the responder’s job is to validate, contain, and remove the threat. This separation matters because ad hoc cleanup often destroys the information needed to determine whether the message was a one-off lure, part of a wider campaign, or evidence of account compromise.
Risk and Threat Considerations
Suspicious messages become more dangerous when people try to handle them manually before the incident is contained. The main risks are loss of forensic evidence, accidental execution of malicious content, and delay while the attacker may still have an active path into the environment.
Failure mechanism: User-side cleanup can remove headers, timestamps, attachments, or preserved copies that investigators need, while also giving the sender extra time if the message is part of an active campaign or compromised account event.
Impact: The organisation can lose visibility into the delivery method, miss related recipients, slow down containment, and make it harder to prove whether the message was merely suspicious or part of a broader compromise.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
MITRE ATT&CK addresses the attack and risk surface, while NIST CSF 2.0, NIST SP 800-53 Rev 5 and CIS Controls v8 set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| NIST CSF 2.0 | RS.CO-01 — Response Planning | Suspicious-message handling depends on coordinated reporting and escalation during an incident. |
| Recommendation — Route suspicious messages through the incident-response reporting path without ad hoc cleanup. | ||
| NIST SP 800-53 Rev 5 | AU-6 — Audit Record Review, Analysis, and Reporting | Preserving message evidence supports review and analysis of indicators and events. |
| Recommendation — Preserve original message artefacts so analysts can review headers, metadata and related indicators. | ||
| CIS Controls v8 | CIS-17 — Incident Response Management | The question is about user handling during incident response and containment. |
| Recommendation — Define a user reporting path that stops interaction and escalates suspicious messages immediately. | ||
| MITRE ATT&CK | T1566 — Phishing | Suspicious messages commonly reflect phishing delivery and social engineering attempts. |
| Recommendation — Treat the message as a suspected phishing delivery and hunt for related recipients or follow-on activity. | ||
Practitioner Guidance
What to verify: Confirm that the reporting path preserves the original message and that users are not asked to sanitize it first. If your process depends on screenshots or manual transcription, it is usually too weak for incident handling because it drops metadata that matters during triage.
Decision rule: If the message may involve a live compromise of email, identity, or another messaging channel, prioritise preservation and alternate-channel coordination before any cleanup. If staff can still reach the approved reporting route, the right action is to escalate, not to investigate on their own.
Practitioner takeaway: The best response to a suspicious message is to keep it intact long enough for containment and analysis, because evidence loss is often more damaging than the message itself.
Related resources from NHI Mgmt Group
- How should organisations handle consent and opt-out requirements before sending direct marketing messages in Australia?
- Why do attackers often check model availability before trying to generate content?
- What should organisations verify before treating acquisition identity integration as complete?
- How should security teams handle compromised Teams messages before users interact with them?