Agentmail

Agentmail is the category of email infrastructure designed for AI agents — dedicated per-agent addresses, structured inbound parsing, prompt-injection scanning, and per-agent reputation, so agents can send and receive email without sharing a human inbox.

The agentmail category emerged as AI agents moved from internal tools to production systems that communicate with humans and other agents over email. Traditional email APIs handle the send side well, but agents need more: a dedicated address per agent, structured parsing of every inbound reply, and security scanning before untrusted email content reaches the agent’s LLM.

What makes agentmail different from transactional email

Transactional email services (SendGrid, Postmark, Amazon SES) are designed for human-initiated, one-directional messages — password resets, order confirmations, marketing campaigns. Agentmail infrastructure adds three layers that transactional providers do not offer:

• Per-agent identity. Each AI agent gets its own email address rather than sharing a single noreply@company.com. Replies route back to the specific agent, threading and reputation attach to that agent, and one agent’s deliverability issues do not affect others. See AI email agent.
• Structured inbound parsing. Raw MIME is unusable for an LLM. Agentmail infrastructure parses every inbound reply into a typed event — extracted reply text, thread context, sender metadata, and an injection score — before the agent’s code processes it.
• Prompt-injection scanning. Email is untrusted input. Agentmail infrastructure scans every inbound for instructions aimed at the agent’s LLM — boundary manipulation, system prompt override, data exfiltration, role hijacking, tool invocation, and jailbreaks — and flags high-risk messages so the agent can skip them.

The agentmail landscape: AgentMail vs Mails.ai

Two platforms define the agentmail category today. AgentMail (agentmail.to) launched first, raised a $6M seed in March 2026, and has 500+ B2B customers. Mails.ai is live and self-serve with a smaller customer base but deeper infrastructure on inbound security and reputation. The key differences, checked October 2026:

• Injection scanning. Mails.ai scans every inbound on every plan. AgentMail’s screening (Agent Armor) is a beta you request, and it starts in observe-only mode.
• Per-agent reputation. Mails.ai tracks reputation per agent with suppression at send time and auto-suspend at 0.3% complaint rate. AgentMail runs per-account reputation only.
• Agent limits. Mails.ai Scale includes unlimited agents. AgentMail’s $20 plan has 10 inboxes; the $200 plan has 150, with $2/month add-ons in between.
• MCP support. Both ship an MCP server for drop-in use in Claude Code, Cursor, and other runtimes.

For the full feature matrix, pricing breakdown, and guidance on when to choose which, see the AgentMail vs Mails.ai comparison.

Core components of agentmail infrastructure

Any agentmail platform needs to provide these primitives for agents to communicate effectively over email:

• Agent inbox creation. Programmatically create a new email identity for each agent via API or SDK. The address should be DNS-authenticated (SPF, DKIM, DMARC) from the start.
• Send API. HTTP-based send that wraps SMTP — the agent passes recipient, subject, and body; the infrastructure handles TLS, DKIM signing, bounce tracking, and retry.
• Inbound webhooks or streaming. Replies to the agent’s address must be delivered to the agent’s code in real time — via webhook, SSE, or long-poll — as structured events, not raw MIME.
• Threading. The infrastructure must track Message-ID, In-Reply-To, and References so multi-turn email conversations maintain context.
• Reputation tracking. Per-agent bounce rates, complaint rates, and send volume tracked independently so one agent’s issues do not degrade another’s deliverability. See sender reputation.
• Security layer. Prompt-injection scanning on every inbound, with a numeric score the agent can threshold against. See injection score.

When to use agentmail vs a traditional email API

Not every agent needs agentmail. The decision depends on whether the agent holds its own email identity and reads untrusted replies:

• Use agentmail when the agent sends email as itself (not as a human), receives replies, and acts on them autonomously. Examples: a support agent, a document-processing agent, a scheduling agent, or any agent that holds an email conversation.
• Use a traditional email API when the application sends transactional email on behalf of humans (password resets, receipts, notifications) and does not need to parse inbound replies programmatically.
• Use both when the application has human-facing transactional email (Postmark, SES) and autonomous agents that hold their own conversations (agentmail via Mails.ai or AgentMail).

Getting started with agentmail on Mails.ai

Sign up at mails.ai/signup — the free tier covers 3,000 emails and 3,000 inbound replies a month with no card. Create an agent, send a message, and receive a typed reply event with injection scoring and sender reputation built in. For agents running in MCP-compatible runtimes (Claude Code, Cursor, Windsurf), the MCP server exposes agentmail capabilities as native tools with a one-line config.

If you are currently on AgentMail and evaluating a switch, the migration guide has a side-by-side code diff and full API mapping table. The SDK shapes are similar enough that migration is typically a half-day exercise.