AgentMail gives agents inboxes over a REST API. MCPmailer gives them the same over MCP, with reply-first quotas and a supervision dashboard.
Agent inbox APIs · AgentMail claims checked July 2026
AgentMail is the closest thing we have to a direct competitor, and it is good. One API call creates an inbox; the agent can send, receive, thread, label, draft, and schedule, with delivery over webhooks and websockets. It has semantic search across inboxes, prompt-driven labeling, and structured extraction from inbound mail, and it has been shipping since 2025 with real volume behind it.
If your agent lives inside your own backend and you would rather call HTTP than speak MCP, AgentMail is a strong choice. Its semantic search and prompt-driven labeling go further than our full-text search, so if analysing inbox content is the feature you are buying, buy theirs.
We start from MCP rather than from HTTP, and we treat the human as part of the system rather than as an afterthought. The tools your agent sees are the surface we design and version, the quotas know the difference between answering a customer and cold-emailing a stranger, and everything the agent ever wrote is readable by a person who is accountable for it.
Both of us can be reached over MCP. The difference is which surface is designed first. Our tool schemas, error strings, and defaults are written for a model reading them cold: a refused send comes back as daily_send_quota_exhausted with the reset time, so the agent can explain itself or wait rather than retry into a wall. When MCP is generated from an HTTP API, that phrasing is inherited from a status code.
Webhooks and websockets are the right primitive for a server you already run. They are the wrong primitive for an agent in a chat client or a cron job, because now something has to be publicly reachable, authenticated, and awake. wait_for_reply long-polls for up to five minutes and returns the reply, so a multi-turn conversation is a loop in the agent rather than a service you deploy.
Past the inbox, our workspace carries a contact book the agent writes facts back into with remember_about_contact, shared notes, and an encrypted vault it reads credentials from with a key that never reaches us. An agent answering its fortieth email from the same customer has somewhere to have learned something.
Every row is a claim we could defend with their documentation open beside it. Where they are ahead, the row says so.
Both products own the mailbox, so this is a cutover rather than a data migration. Run them side by side on different addresses until you trust it.
Recreate the inboxes
One agent per mailbox, same local parts. On the free tier you get three, on a subdomain you get instantly.
Point the domain, or do not
You can keep sending from you.mcpmailer.email while you test, then verify agents.yourcompany.com when you are ready to move the reputation.
Replace the SDK calls with MCP tools
send_email, list_messages, read_message, and get_thread cover the AgentMail equivalents. If your stack cannot speak MCP, the REST API at /v1 takes the same keys.
Delete your webhook handler
The endpoint you were hosting to catch inbound mail becomes a wait_for_reply call, or nothing at all if the agent polls list_messages on its own schedule.
If what you liked about AgentMail was the per-agent inbox but you want MCP as the first-class surface, a supervision dashboard, and quotas that separate replies from cold outreach, that is this. If you specifically wanted semantic search over inbox content, no alternative including us matches it yet.
It is the only interface we design against, so yes in the sense that matters: tool naming, error strings, and defaults are written for a model rather than generated from an HTTP surface. AgentMail's MCP support is real, it just is not where its product decisions get made.
The free tiers are the same shape: 3,000 emails a month, 100 a day, 3 inboxes, no card. AgentMail publishes a $20 developer plan and a $200 startup plan; ours are $20 and $200 as well, so at small scale this is not a price decision. Compare on where the conversation state lives instead.
Yes, and it is the sane way to evaluate. Use separate addresses on separate domains so the two sending reputations never mix, then move traffic once you have watched a real thread play out in both.
If you are choosing between agent inbox APIs, the deciding question is usually where the conversation state lives. Ours lives in the mailbox, and your agent reaches it with tools instead of with a schema you maintain.
The free tier is 3,000 emails a month across three agent inboxes, no card, with receiving, threading, and search included. Enough to watch a real conversation happen before you decide.
More Agent inbox APIs