Email Removal & Blocking

1. Prerequisites

• IOCs identified during triage and analysis:
  • Sender domains
  • Email subjects
  • URLs
  • Attachment hashes
  • Message IDs
  • Campaign indicators
• Access to Microsoft 365
• Access to Google Workspace
• Access to Secure Email Gateway (SEG)
• Access to DNS / proxy platform

2. Step-by-Step Instructions

1. Identify All Matching Emails

   • Locate delivered messages
   • Locate quarantined messages
   • Locate forwarded copies
   • Locate internal relay copies

2. Remove Emails from Mailboxes

   • Perform tenant-wide remediation:
     • Delete phishing emails
     • Purge from inboxes
     • Remove from deleted items if required
   • Validate removal success.

3. Block Sender Infrastructure

   • Block:
     • Sender domains
     • Reply-To domains
     • Sending IPs
     • Known malicious infrastructure

4. Block URLs

   • Add blocks at:
     • Secure Email Gateway
     • DNS filtering
     • Proxy
     • Browser isolation platform (if applicable)

5. Block Attachments / Hashes

   • Prevent delivery or execution of:
     • Malicious hashes
     • File types associated with campaign

6. Deploy Temporary Detections

   • Add detections for:
     • Similar subjects
     • Similar domains
     • Similar URLs
     • Behavioural patterns

7. Validate Effectiveness

   • Confirm:
     • No remaining emails exist
     • Blocks are active
     • Users cannot access malicious infrastructure

3. Post-Action

• Note down time of email removals and blocking in the incident ticket

Contributor

Vishal Thakur
GitHub: https://github.com/malienist

Jayden Vo GitHub: https://github.com/jayden-vo

Contributed to the Arcana Incident Response Documentation Framework.