Overview
Phishing remains the most common initial access vector for cyber attacks, and every reported phishing email is an intelligence opportunity. This playbook provides step-by-step procedures for analyzing reported phishing emails, from header inspection through payload analysis and IOC extraction. Follow it consistently and you will turn user reports into actionable intelligence that improves your defenses.
Analysis Workflow
- Receive the reported email and preserve the original with full headers
- Analyze email headers to identify the true sending infrastructure
- Inspect URLs without clicking: use sandbox or URL expansion tools
- Check sender reputation against threat intelligence and blocklists
- Analyze any attachments in a sandboxed environment
- Extract IOCs: sender domains, IPs, URLs, file hashes, email subjects
- Determine the intent: credential harvesting, malware delivery, BEC, or reconnaissance
- Check if other users received the same or similar emails
- Take containment actions: block domains, quarantine matching emails, reset credentials if needed
- Document findings and close the ticket
Header Analysis Fields
| Header field | What to check | Red flags |
|---|---|---|
| Return-Path | Actual reply destination | Mismatch with From address |
| Received | Mail server path and originating IP | Suspicious or unknown mail relays |
| Authentication-Results | SPF, DKIM, DMARC pass/fail | Failures on supposedly legitimate senders |
| X-Originating-IP | True source IP of the sender | IP from known malicious ranges, VPN, or hosting providers |
| Reply-To | Where replies are directed | Different domain from the From address |
| Message-ID | Unique identifier for the email | Message-ID domain does not match sender domain |
URL and Link Analysis
Never click links directly. Copy the URL and analyze it in a sandboxed tool like URLScan, VirusTotal, or your SOAR platform. Look for domain spoofing techniques like typosquatting, homoglyph attacks, and subdomain abuse. Check when the domain was registered because newly created domains are a strong phishing indicator. Inspect URL shorteners by expanding them before analysis. Compare the visible text of the link with the actual href destination and flag mismatches. Pay attention to redirects that chain through multiple domains before reaching the final landing page.
Attachment Analysis
- Submit attachments to a malware sandbox for behavioral analysis before opening them
- Check file hashes against threat intelligence databases and VirusTotal
- Analyze file metadata for suspicious properties: authorship, creation tools, hidden macros
- For Office documents, check for embedded macros, OLE objects, and external template references
- For PDFs, inspect for embedded JavaScript, launch actions, and suspicious form fields
- For archive files (ZIP, RAR, 7z), check for password protection (often noted in the email body) and nested payloads
Containment and Response
Once you confirm a phishing email is malicious, move fast. Search your email platform for all instances of the same email by subject line, sender, or unique body content. Quarantine or purge matching messages from all mailboxes. Block the sender domain and any malicious URLs at the email gateway and web proxy. If any user clicked a link or opened an attachment, treat it as a potential compromise: reset their credentials, scan their endpoint, and check for post-exploitation activity. Report the IOCs to your threat intelligence platform so future emails from the same campaign are caught automatically.
