---
title: IMAP, SMTP, REST, MCP, or A2A for an AI agent?
description: A protocol guide for choosing how agents send, receive, discover, and delegate communication work.
canonical: https://agentmailer.ai/blog/imap-smtp-rest-for-ai-agents
last-updated: 2026-08-25
---

# IMAP, SMTP, REST, MCP, or A2A for an AI agent?

> A protocol guide for choosing how agents send, receive, discover, and delegate communication work.

## Direct answer

Use REST for direct product integration, MCP when a model client needs discoverable tools, A2A for structured agent-to-agent tasks, IMAP for compatibility with mailbox clients, and SMTP for compatibility with existing senders. These protocols solve different layers and can share one mailbox identity.

## REST for application control

REST is the straightforward choice for provisioning inboxes, listing threads, sending replies, managing labels, and configuring webhooks from your backend. It exposes stable resources and works well with typed SDKs.

## MCP for model-facing tools

MCP lets a compatible agent client discover email tools and invoke them with structured inputs. It reduces one-off tool wrappers, while authorization and workspace scope remain enforced by AgentMailer.

## A2A for agent delegation

A2A describes an agent and supports structured messages and tasks. It complements email: use email when the counterparty is a person or existing service, and A2A when another agent can accept a structured task directly.

## IMAP and SMTP for compatibility

IMAP gives existing clients and libraries access to mailbox state. SMTP lets legacy software submit messages. They are essential compatibility surfaces, but a new agent integration usually benefits from the richer identity, threading, event, and authorization model in REST or MCP.

## Frequently asked questions

### Does MCP replace IMAP?

No. MCP exposes model-friendly tools; IMAP exposes standard mailbox access. They serve different clients.

### Does A2A replace email?

No. A2A improves structured agent communication, while email remains the broadly compatible channel for people and existing services.