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mail-server-hardening

Audit SMTP, IMAP, POP3, ManageSieve, and mailbox-DAV listeners for protocol-layer security gaps.

Updated May 11, 2026
Search Tags:#open relay#protocol security#compliance gaps#mail server hardening#smtp smuggling#starttls injection#imap hardening
One-click install
npx skills add https://github.com/blamejs/exceptd-skills --skill mail-server-hardening
Or copy as Structured Prompt for Agent▼
Please help me install this Agent Skill.
Skill: mail-server-hardening
Source: https://github.com/blamejs/exceptd-skills/tree/main/skills/mail-server-hardening
Command: npx skills add https://github.com/blamejs/exceptd-skills --skill mail-server-hardening

SYSTEM DOCUMENTATION & REQUIREMENTS

What problem does it solve?

Standard mail security controls including SPF, DKIM, DMARC, and transport TLS fail to protect the inbound mail server protocol layer from attacks like SMTP smuggling, STARTTLS command injection, open relay, and mailbox data exfiltration, leaving organizations vulnerable to spoofing, reputation abuse, and data breaches that standard compliance audits often miss.

Core Features & Use Cases

  • Protocol Layer Auditing: Detects hardening gaps across SMTP, IMAP, POP3, ManageSieve, and mailbox-DAV (CalDAV/CardDAV) listeners that standard security checks overlook.
  • Compliance Gap Mapping: Identifies where common frameworks (NIST 800-53, ISO 27001, NIS2, PCI-DSS) lack controls for modern mail protocol attack vectors.
  • Prioritized Remediation: Delivers actionable fixes and negative validation tests to confirm each hardening control works as expected. Use Case: A security team running an inbound mail server can use this skill to audit for SMTP smuggling and open relay gaps, prove their existing DMARC and TLS controls do not cover protocol-layer risks, and implement targeted fixes to prevent spoofing and exfiltration.

Quick Start

Use the mail-server-hardening skill to audit your organization's inbound mail listeners for protocol-layer security gaps and receive prioritized remediation steps.

Frequently Asked Questions about mail-server-hardening

High-intent search queries and answers about installing and using this skill.

FAQPage Schema
How do I detect SMTP smuggling and STARTTLS injection vulnerabilities on my mail server?▼

Mail server hardening protects against protocol attacks like SMTP smuggling, STARTTLS command injection, open relay, and mailbox data exfiltration. It secures inbound listeners by identifying weaknesses unaddressed by standard SPF, DKIM, DMARC, and TLS controls.

Can I map mail server protocol vulnerabilities to compliance frameworks like NIST 800-53 or ISO 27001?▼

You can map protocol vulnerabilities to compliance frameworks like NIST 800-53, ISO 27001, NIS2, and PCI-DSS. This mapping identifies specific control deficiencies for modern mail protocol attack vectors to ensure comprehensive compliance gap coverage.

How do I audit ManageSieve and mailbox-DAV listeners for data exfiltration gaps?▼

To audit ManageSieve and mailbox-DAV listeners, you scan for Sieve redirect exfiltration, traversal, and XXE gaps. This protocol layer auditing detects vulnerabilities across CalDAV and CardDAV services that standard security checks often overlook.

Does standard DMARC and TLS protect against command injection on IMAP and POP3?▼

Standard DMARC and TLS do not protect against command injection on IMAP and POP3. They fail to secure the inbound mail server protocol layer, leaving organizations vulnerable to spoofing and data breaches that compliance audits miss.

What is the best way to remediate open relay and SMTP smuggling vulnerabilities after detection?▼

The best way to remediate open relay and SMTP smuggling is to implement prioritized fixes based on MITRE ATT&CK and CWE mappings. You then run negative validation test cases to confirm each hardening control works as expected.

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