AgentMail (YC S25, $6M seed March 2026) and MailSink both ship MCP servers that give AI agents real email capability. But they answer a different product question. AgentMail says “your agent is a persistent identity with a real inbox”. MailSink says “your agent’s task is one-shot; give it a throwaway inbox and move on”.
Both companies are early-stage 2025 launches. AgentMail is a YC-backed San Francisco team focused on the persistent-agent-identity model. MailSink is an indie-funded project optimized for the one-shot test/automation use case. They co-rank on the same query (“best temp email API for AI agents”) but serve different needs.
Neither is wrong; they serve different workflows. This post shows how to pick.
TL;DR
| AgentMail | MailSink | |
|---|---|---|
| Inbox model | Persistent, agent-bound | Temporary, task-bound |
| TTL | Indefinite | 1 hr to 7 days |
| Identity | Stable across sessions | One-shot per test/signup |
| MCP server | Yes | Yes (@mailsink/mcp) |
| Best at | Named agents that receive mail over time | Signup flows, test automation, CI |
| Pricing model | Flat tiers ($0 / $20 / $200) + Enterprise usage-based | Flat tiers ($0 / $15 / $49) |
| Send capability | Yes (agent can reply with threading) | No (v1 receive-only) |
| Funding / maturity | YC S25, $6M seed (Mar 2026), team of 8 | Indie, self-funded |
If your agent needs to keep a conversation going with a human or another service over days or weeks, AgentMail. If your agent needs an inbox for a specific task and then you’d like it to disappear, MailSink.
The product question each answers
AgentMail’s bet
If an AI agent is a named actor in a system (a “customer support specialist”, a “lead-gen worker”, a “legal researcher”), it needs an inbox that persists. People email agents. Other services send notifications to agents. The inbox becomes the agent’s memory over time.
AgentMail’s product shape follows:
- Persistent inbox per agent
- Send capability so the agent can reply
- Thread continuity across messages
- Identity-linked pricing (usage-based per agent)
This is the right model when the agent’s job is ongoing conversation with an external party.
MailSink’s bet
If an AI agent’s task is one-shot (sign up for a service, catch an OTP, complete a form, disappear), a persistent inbox is over-engineering. Every task should get a fresh address bound to that task, and the address should clean up afterward to avoid accumulating cruft.
MailSink’s product shape:
- Disposable inbox per task
- Auto-expire via TTL (1 hr to 7 days)
- Account-scoped addresses
- Flat plan pricing (no per-inbox or per-message fees)
This is the right model when the agent’s job is an automated workflow that should leave no trace.
Side by side
Identity and state
AgentMail: each inbox is long-lived. Agent A gets [email protected] (or similar), and that address stays attached to Agent A across sessions.
MailSink: each inbox is throwaway. A single account can provision many inboxes. Names are {tag}-{6-char-random}@{shared-domain}. Nothing about the address tells you which agent owns it beyond the account-level ownership in the database.
If you want every CI run to get its own inbox and you don’t want old messages piling up, MailSink’s model fits. If you want a support-agent identity that users can email at a stable address, AgentMail.
Retention
AgentMail: persistent. Messages stay. You manage retention yourself (archive, delete via API).
MailSink: TTL-based. Messages and inboxes delete automatically. Free: 1 hour. Pro: 24 hours. Team: 7 days. After TTL, R2 blobs and D1 metadata are both purged.
Sending
AgentMail: agents can send. The inbox is bidirectional.
MailSink: v1 is receive-only. Your agent reads incoming mail. Sending from MailSink addresses is not supported today. If your workflow needs the agent to reply, AgentMail is the right fit.
MCP ergonomics
Both ship MCP servers. Tool shapes are similar:
| AgentMail (approx) | MailSink |
|---|---|
create_inbox | create_inbox |
get_inbox_messages | list_messages |
get_message | get_message |
send_email | (not supported) |
wait_for_reply | wait_for_email, wait_for_code, wait_for_link |
MailSink’s extractors (get_verification_code, get_verification_link) give you a “just give me the OTP” one-call path that’s absent in AgentMail’s verb set. If your agent’s main job is catching verification codes, that’s nicer. If your agent’s main job is threading replies, you want AgentMail’s send_email.
Pricing
Both are flat-tier (verified May 2026):
| Tier | AgentMail | MailSink |
|---|---|---|
| Free | $0 — 3 inboxes, 3,000 emails/mo, 100/day cap | $0 — 50 inboxes/mo, MCP included |
| Mid | Developer $20 — 10 inboxes, 10,000 emails/mo | Pro $15 — 2,000 inboxes/mo |
| Scale | Startup $200 — 150 inboxes, 150,000 emails/mo | Team $49 — 20,000 inboxes/mo |
| Enterprise | Custom + usage-based option | Contact for volume |
The shapes are different because the products are different. AgentMail charges for persistence and storage (each inbox is long-lived with mail accumulating). MailSink charges for throughput (each inbox is short-lived; volume is the cost driver, retention isn’t).
For burst CI workflows that need thousands of throwaway inboxes per month, MailSink’s $49 Team plan undercuts AgentMail’s $200 Startup at 20K inboxes/mo. For a handful of persistent agent identities with steady mail volume, AgentMail’s $20 Developer tier fits.
Use-case matrix
| Workflow | Best fit |
|---|---|
| CI signup tests (Playwright, Cypress, Selenium) | MailSink |
| AI agent signs up for a third-party service for a user | MailSink |
| Agent runs QA regression suite | MailSink |
| Support agent that replies to user emails over time | AgentMail |
| Lead-gen agent that nurtures inbound leads | AgentMail |
| Long-running research agent with a known email address | AgentMail |
| One-shot data-collection task that should leave no trace | MailSink |
Can you use both?
Absolutely. They’re not competing for the same slot in an agent’s toolkit. An agent fleet might use AgentMail for the customer-facing support persona and MailSink for one-off signups it does during research. The MCP spec allows multiple email servers to be configured alongside each other; each tool name is namespaced.
When to move between them
If you started with AgentMail for testing purposes but your retention is accumulating and you don’t need the conversation continuity, MailSink’s TTL model is probably what you wanted. If you started with MailSink but keep manually recreating inboxes for the same agent identity, AgentMail’s persistence is the right call.
FAQ
Can MailSink send email?
Not in v1. Send capability is on the roadmap if customer demand signals it. Today MailSink is receive-only.
Does AgentMail have extractors like MailSink’s get_verification_code?
Not as a first-class tool as of April 2026. You can fetch a message and parse in the agent, but there’s no equivalent single-call path for “just return the OTP”.
Does the MCP spec allow multiple email servers at once?
Yes. Claude Desktop, Claude Code, and Cursor all support running several MCP servers simultaneously. Tool names are namespaced by server, so mailsink:create_inbox and agentmail:create_inbox coexist without confusion.
Which one is cheaper?
Depends on workload. For CI-heavy workflows that burst to thousands of inboxes per month, MailSink’s flat $49 Team plan is cheaper than AgentMail’s per-inbox/per-message billing at that volume. For low-volume agent-identity workflows (a handful of persistent inboxes), AgentMail may be cheaper.
What about BYOD (custom domains)?
AgentMail supports it on paid plans. MailSink has BYOD on the waitlist for Pro+.
Next
- Try MailSink free (50 inboxes/month, MCP included)
- MCP server setup guide
- MailSink vs Mailtrap (different category entirely)
- MailSink vs MailSlurp
- AgentMail for their latest docs and pricing