What Is an Email Gateway? (And Why Prompt Injection Detection Matters)
As businesses integrate AI into their workflows, a new threat has emerged: prompt injection via email. Attackers are embedding malicious instructions in emails to manipulate LLM-powered assistants and automation tools.
An AI-powered email gateway is your first line of defense. This guide explains what email gateways do, how they categorize inbound mail, and why prompt injection detection is now essential.
What Is an Email Gateway?
An email gateway sits between the public internet and your mail server. It inspects, categorizes, and filters every incoming email before it reaches your inbox.
Traditional email gateways focus on spam and malware. Modern AI-powered gateways go much further:
- Semantic categorization (cold outreach, warm lead, support, partner)
- Intent detection
- Prompt injection scanning
- Smart header injection for CRM filtering
- Transparent SMTP relay
How AI Email Categorization Works
Instead of relying on simple keyword rules, AI email gateways use large language models to understand the meaning of each email.
Categories Include:
- Cold Outreach: Unsolicited sales or partnership pitches
- Warm Lead: Inbound interest from prospects
- Support: Customer service requests
- Partner: Vendor, affiliate, or integration opportunities
- Internal: Team communications
- Other: Uncategorized messages
These categories are injected as headers (e.g., X-Gateway-Category: cold), allowing you to build powerful filters in Gmail, Outlook, or your CRM.
What Is Prompt Injection?
Prompt injection is an attack where malicious instructions are hidden inside user input (like an email) to override an AI system's behavior.