MailSlurp has been doing email testing for years and does it well: unlimited inboxes on paid plans, disposable addresses, SMTP and IMAP, device rendering, inbox placement tests, an AI extraction feature and SAML/OIDC single sign-on at the enterprise tier. As a QA tool it is more mature than most of the agent-email startups on this site.
Bottom line: the allowances are sized for tests, not traffic. The $49.99 Pro plan allows 5,000 received emails a month and 500 sends to external addresses; the $129.99 Growth plan allows the same 5,000 received. A single production support agent handling a few hundred threads will exhaust that in a week. Dead Simple Email's $29 plan carries 100,000 emails and its $99 plan carries 500,000 — a hundred times the volume for less money.
Pricing Comparison
Figures as read on 2026-09-16.
| Tier | Dead Simple Email | MailSlurp |
|---|---|---|
| Free | 5 inboxes · 5,000 emails/mo | 50 retained inboxes · 500 received · 200 MB |
| Entry paid | $5/mo — 15 inboxes, 15,000 emails | $19.99/mo — 100 inboxes, 1,000 received, 100 test sends |
| Mid | $29/mo — 100 inboxes, 100,000 emails | $49.99/mo — unlimited inboxes, 5,000 received, 500 external sends |
| Top published | $99/mo — 500 inboxes, 500,000 emails | $129.99/mo — unlimited inboxes, 5,000 received, 2 users |
| Emails per dollar at the top tier | ~5,050 per $1 | ~38 per $1 |
| External sending | Unlimited within plan | 500/mo on Pro and Growth |
MailSlurp's unlimited-inbox model is genuinely useful — but inboxes are not the scarce resource for an agent fleet. Messages are, and that is the axis where the two products differ by two orders of magnitude.
Feature Comparison
| Feature | Dead Simple Email | MailSlurp |
|---|---|---|
| Emails included at the top published plan | 500,000/mo | 5,000 received/mo |
| External sending | Unlimited within the plan allowance | 500/mo |
| Inbox count | 5 / 15 / 100 / 500 by plan | Unlimited on Pro and above |
| IMAP / SMTP | Yes | Yes |
| MCP server | Yes — in the official MCP registry | Not advertised |
| Webhooks | All plans, with delivery log and replay | Yes |
| Prompt-injection scanning | Yes — scored on every inbound | No |
| Verification-code / OTP extraction | Yes — dedicated endpoint, free on all plans | AI extraction, metered at $1.00 per 10,000 weighted tokens |
| Device rendering / inbox placement tests | No | Yes — the core QA feature set |
| Framework integrations | LangChain, CrewAI, AutoGen, LlamaIndex, Vercel AI SDK and more | Test-framework integrations |
| Agent identity / OIDC sign-in | Yes — Sign in with Dead Simple | SSO for logging in to MailSlurp |
| Pay per request without an API key | Yes — x402 USDC and Stripe MPP | No |
Where MailSlurp Wins
- QA tooling. Device rendering across Apple Mail, Outlook desktop and Gmail, plus inbox placement testing, are features Dead Simple Email does not build and is not planning to. If you are checking how a marketing template renders, MailSlurp is the right tool.
- Unlimited disposable inboxes. For a test suite creating and destroying hundreds of addresses per run, an unlimited inbox count with a small message allowance is exactly the right shape.
- Maturity. It has been running for years, with SSO and a large customer base. Most agent-email vendors, this one included, are younger.
Who Should Use Dead Simple Email
- Any agent in production. 5,000 received emails a month is a test budget, not a traffic budget.
- Agents that send. 500 external sends a month on MailSlurp's paid plans; unlimited within your allowance on Dead Simple Email.
- MCP-native stacks. Email as first-class tools in Claude, Cursor and any MCP client.
- Agents that read untrusted mail, which need injection scanning and free verification-code extraction rather than token-metered AI extraction.
Frequently Asked Questions
As of September 2026, 500 received on the free plan, 1,000 on the $19.99 Starter plan, and 5,000 on both the $49.99 Pro and $129.99 Growth plans, with 500 sends to external addresses on the paid tiers. Dead Simple Email includes 5,000 emails a month on its free plan and 500,000 on its $99 plan.
For testing agents, yes — unlimited disposable inboxes are ideal for CI. For running them, the message allowances are the constraint: a production agent handling real conversations will pass 5,000 messages a month quickly, and MailSlurp's largest published plan does not go higher.
Dead Simple Email. It gives every agent a persistent inbox with IMAP and SMTP, HMAC-signed webhooks, an MCP server in the official registry, prompt-injection scanning and free verification-code extraction, with 100,000 emails on the $29 plan and 500,000 on the $99 plan.
Yes, and it is included rather than metered. Every inbox exposes an endpoint returning the latest one-time code, magic link or confirmation URL, free on every plan including the free tier. MailSlurp's AI extraction is billed at $1.00 per 10,000 weighted tokens as of September 2026.
Not as an advertised feature as of September 2026. Dead Simple Email publishes an MCP server listed in the official MCP registry, with OAuth 2.1 support, so agents in Claude, Cursor and other MCP clients get email as native tools.
Yes. A common split is MailSlurp for email QA and test-suite inboxes, Dead Simple Email for the inboxes agents own in production. Dead Simple Email's free plan also covers modest test suites at 5 inboxes and 5,000 emails a month.
All MailSlurp figures on this page were read from its public pricing page on 2026-09-16 and are reproduced for comparison. Vendors change prices; check the source before making a decision, and tell us if anything here is out of date. Full cross-vendor tables: AI agent email API pricing comparison.