# Lumbox vs MailSlurp

> MailSlurp scores 66.7 (B) to Lumbox's 60.7 (C) for agent inboxes. Prices, MCP, x402, uptime and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/lumbox-vs-mailslurp
- Markdown: https://www.anchorterminal.com/compare/lumbox-vs-mailslurp.md (~4,750 tokens)
- Site index for agents: https://www.anchorterminal.com/llms.txt (the key docs and every listing in one file, at most 16 MB, about 4 million tokens: https://www.anchorterminal.com/llms-full.txt)
- API: https://www.anchorterminal.com/api/v1/index.json
- MCP: https://www.anchorterminal.com/mcp (the whole catalogue as tools, no key)
- DNS: dig +short TXT <slug>.grade.anchorterminal.com (the grade as a DNS TXT record, for a sandbox with no HTTP where names still resolve; also top., best.<category>. and <a>.vs.<b>. under the zone, and the same under grade.letme.dev)
- Licence: CC BY 4.0, credit Anchor Terminal and link this page (https://www.anchorterminal.com/terms/#data)
- Updated: 2026-11-07

MailSlurp scores 66.7 (B) on agent readiness against Lumbox's 60.7 (C), and leads in 3 of 7 scored categories. Lumbox leads on schema & documentation, payments & pricing and transparency & trust. Both do agent inboxes.

- Lumbox: grade C, 60.7/100, rank #645 of 1510. Markdown https://www.anchorterminal.com/tools/lumbox.md · JSON https://www.anchorterminal.com/api/v1/tools/lumbox.json
- MailSlurp: grade B, 66.7/100, rank #359 of 1510. Markdown https://www.anchorterminal.com/tools/mailslurp.md · JSON https://www.anchorterminal.com/api/v1/tools/mailslurp.json
- Best email inbox APIs for AI agents: https://www.anchorterminal.com/best/agent-inboxes/index.md
- All 66 inboxes comparisons: https://www.anchorterminal.com/compare/agent-inboxes/index.md

## Which one, for what

### Lumbox (C)

Good for: Agents that need their own address to receive sign-up codes and links and to send replies.

Ahead on:
- Schema & documentation, 82 against 72
- Payments & pricing, 40 against 32
- Transparency & trust, 72 against 60

Also in its favour:
- Runs on your own machine
- Free to start without a card

Watch for: No status page, incident history or SLA; the terms say availability isn't guaranteed

### MailSlurp (B)

Good for: QA and test agents that read OTP, verification and reset mail, and for supervised support agents where a person approves drafts.

Ahead on:
- Reliability, 75 against 45
- Agent ergonomics, 84 against 78
- Maintenance & community, 55 against 23

Watch for: Free sends only to inboxes in the same account and Starter only within MailSlurp. External sending and custom domains start on Pro at $49.99 a month


## Why the edge

### Maintenance & community: MailSlurp +32

- Lumbox (23): The latest package releases found are lumbox 0.3.1 on npm (19 June 2026) and @lumbox/mcp-server 0.2.2 (12 June 2026), 140 days before this check, the 91 to 180 day band (10). No releases or dated changelog entries in the 90 days from 8 August (0). A closed service with a support address and an X account; no changelog (5 of 15). Not in the official MCP registry (search for lumbox returned nothing on 6 November); Node and Python SDKs exist but haven't changed since June (5 of 15). The MCP server card says 0.2.1 while npm has 0.2.2, and the SDK repository named in npm isn't publicly readable (3 of 10). Total 23.
- MailSlurp (55): Official SDK releases 17.6.0 for Python, Java, Go and PHP were tagged on 26 October 2026, each regenerated with code changes, and the listed `mailslurp-client` for JavaScript on 24 September (30). Since 3 August those are the only dated releases, five SDK tags that count half each (2.5), and there is no public API changelog, so the line for three in 90 days isn't met. The 9 October check met it with v17.3.0 and v17.4.0 of 14 July, which have left the window (0). Closed service with no public API changelog. A support page and a public board for product requests are linked, and we did not test support (6 of 15). The JavaScript, Python, Java, Go and PHP clients are at 17.6.0, while Ruby and C# stay at 17.5.0 from 31 March (13 of 15). The JavaScript client's tests moved to Vitest on 24 September. Its CI status was not read (6 of 10).

### Reliability: MailSlurp +30

- Lumbox (45): Graded with the hosted lines. No status page was found; none is linked from the site or llms.txt, and status.lumbox.co doesn't resolve (0). With no history to read, the incident line takes 5. 120 requests a minute per API key, per IP for unauthenticated routes, with X-RateLimit headers (15). 429 returns `retry_after_seconds`, the spec gives a backoff schedule and says which statuses not to retry, and `Idempotency-Key` works on every POST for 24 hours (15). The terms say Lumbox doesn't guarantee uninterrupted service, and no SLA was found (0). The core API carries no beta label; dedicated phone numbers are early access (10). Total 45.
- MailSlurp (75): Graded as a hosted service, on the REST API. status.mailslurp.com is an updown.io page with eight checks, among them the API, email processes, IMAP and SMTP. It shows one month of uptime per check and has no incident log (14 of 20). All eight checks read 100 per cent for 9 September to 9 October 2026 on the 9 October check and for 1 October to 1 November on 1 November, though the API check's "up since" time of 28 October 06:03 UTC shows a short interruption before it. The page shows nothing older, so 3 August to 9 September couldn't be read and the 90-day record is only partly readable (20 of 30). A guide states a limit of 150 requests a second and the pricing page gives monthly quotas per plan. The errors and limits page in the docs has no numbers (13 of 15). The docs describe `retryable`, `retryAfterSeconds` and `Retry-After` on some 429s, warn that 429 also means a plan or sending restriction, and advise bounded backoff. Agent reply, draft send and SMS send operations take an `Idempotency-Key` header (14 of 15). An Enterprise page says MailSlurp targets 99 per cent uptime for the core API, and section 9.2 of the terms says no SLA applies without a signed amendment (4 of 10). No beta label on the API or the MCP server, which reported version 1.5.0 on 9 October (10). The limits, SLA and MCP pages are per the 9 October check, not re-read on 1 November.

### Transparency & trust: Lumbox +12

- Lumbox (72): A closed hosted service; the security page says it can be self-hosted, but the repository the deployment guide clones isn't publicly readable. The footer names Cyphen Innovations Private Limited (15 of 30). The privacy policy and security page agree that mail is kept while its inbox exists and an account's data is deleted within 30 days, that email isn't used for training, and that the vault uses AES-256-GCM per-organisation keys (26 of 30). A deprecation policy with Deprecation and Sunset headers, 90 days' notice and 12 months for an old version (20). Hosts and locations named, Hetzner in Germany, Neon in the US, Vercel, Cloudflare, AWS SES, Dodo Payments and Steel for browsers (18 of 20). Total 79.
- MailSlurp (60): Closed service under published terms, with an MIT JavaScript client (17 of 30). One legal document dated 16 January 2026 holds the privacy policy and the DPA. It gives no retention periods and says MailSlurp does not guarantee data retention. Section 7.5.1 promises 14 days' notice of a new sub-processor and section 8.4 says no advance notice is required. The AI disclosure makes no statement on whether AI inputs are kept or used for model improvement by third parties (12 of 30). Nine operations are marked deprecated in the OpenAPI file with no dates, and no deprecation policy was found (4 of 20). The security policy names AWS us-west-2. The trust centre lists four subprocessors and no payment or AI model provider, while the privacy policy names payment processors and analytics providers as recipients (12 of 20).

### Schema & documentation: Lumbox +10

- Lumbox (82): OpenAPI 3.1 at lumbox.co/openapi.json with 29 operations on 23 paths, all described (25). llms.txt with plan limits, endpoints and the MCP setup (10). Descriptions state what each call does, with notes such as long-poll endpoints being safe to retry; the MCP server card gives one line per tool (15 of 20). Typed parameters with `limit` and `cursor`, required fields marked (12 of 15). Shared responses for 400 to 429 and a default error on 28 operations, but errors are a bare `error` string with no code (12 of 15). Path versioning and a written deprecation policy, but the changelog it refers to wasn't found (8 of 15). Total 82.
- MailSlurp (72): OpenAPI 3.0.1 at `api.mailslurp.com/v2/api-docs/`, version 6.5.2, 846 operations on 676 paths on 1 November 2026 (25). `llms.txt` and a Markdown copy linked from each docs page (10). 339 of 846 operations have no description and 93 no summary. The 61 `/agent` operations all have a summary and most name the permission checked. The MCP tool definitions need a credential and were not read (12 of 20). 618 enums, required fields, `uuid` and `date-time` formats and size maxima. Inbox creation takes its options as query parameters and the error `details` field is a free object (12 of 15). Only seven operations document a non-2xx response, four agent work-item calls and three downloads with a `default` response. The docs have a table of status codes and next actions, the file has an `AgentApiErrorDto` schema, and the SDK pages carry examples (8 of 15). The file carries a version number and marks nine operations deprecated. No API changelog was found, and the JavaScript client's CHANGELOG.md has no dates and jumps from 15.12.0 to 17.5.0 (5 of 15). The docs also name `/account/agent-api-keys` paths that are not in the file.

### Payments & pricing: Lumbox +8

- Lumbox (40): No x402, MPP or L402 (0). Four plans with prices and limits published without login, no per-email price (10 of 20). Free plan with 3 inboxes, 500 received and 100 sent emails a month, no card (20). Agent self-signup lets an agent create its own key, which a person approves once in a browser (10 of 20). Total 40.
- MailSlurp (32): No x402, MPP or L402 found (0 of 40). Four plan prices are public, with unit rates for extra device renders, placement tests and AI extraction. The phone and SMS rate table was empty in the page we read, and usage billing for inbox creations beyond a plan has no stated rate (15 of 20). A Free plan at $0 with 500 emails received a month. The page does not say whether signup asks for a card, and we did not sign up (17 of 20). A person signs up in a browser and creates the first key in the dashboard. Agent keys can then be created by API with an account key (0 of 20).

### Agent ergonomics: MailSlurp +6

- Lumbox (78): 18 MCP tools, the 11 to 30 band; OAuth scopes narrow what a grant can do, but no read-only tool subset was found (15 of 25). Cursor pagination with `limit` and `has_more`, search, and an SSE stream for new mail (20). Errors are a human-readable message with the HTTP status, plus `retry_after_seconds` on 429 and written guidance on what to retry (12 of 20). `Idempotency-Key` on every POST; MCP annotations weren't readable without a session (16 of 20). One POST creates an inbox with a default address; official Node and Python SDKs (15). Total 78.
- MailSlurp (84): Graded on the REST API, with the MCP server noted. Agent lists return previews with `size` defaulting to 20 and capped at 100, and `GET /agent/emails/{emailId}/summary` returns a compact message. The MCP docs list 16 tools, whose definitions were not read (20 of 25). `page`, `size`, `sort`, `since` and `before` on lists, a search operation per inbox and wait operations with a deadline (20). Agent errors carry `code`, `message`, `retryable`, `suggestedAction` and `requestId`. The docs say these fields are not on every failure, and the OpenAPI file documents no error response (15 of 20). `Idempotency-Key` on ten operations, among them agent replies, draft sends and SMS sends, plus `expectedConversationVersion` on replies. The standard send operation has none, and MCP annotations were not read (14 of 20). `POST /inboxes` needs no parameter, and the docs list SDKs for ten languages (15).

## Score by category

| Category | Weight | Lumbox | MailSlurp | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 45 | 75 | MailSlurp +30 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 82 | 72 | Lumbox +10 |
| Agent ergonomics | 13% (16.2 this run) | 78 | 84 | MailSlurp +6 |
| Security & auth | 14% (17.5 this run) | 71 | 70 | Lumbox +1 |
| Payments & pricing | 10% (12.5 this run) | 40 | 32 | Lumbox +8 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 23 | 55 | MailSlurp +32 |
| Transparency & trust | 7% (8.8 this run) | 72 | 60 | Lumbox +12 |
| Negative events | ≤15 | 0 | 0 | |
| **Total** | | **60.7 · C** | **66.7 · B** | |

## Facts side by side

| Fact | Lumbox | MailSlurp |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Cyphen Innovations Private Limited | Pettman OÜ |
| Hosted endpoint | `https://mcp.lumbox.co/mcp` | `https://api.mailslurp.com` |
| Transports | HTTP, Streamable HTTP, stdio | HTTP, Streamable HTTP |
| Auth | OAuth or key | OAuth or key |
| Pricing | Freemium | Freemium |
| Price for agent inboxes | not published | $1 per transaction |
| x402 | no | no |
| Licence | none | Proprietary service under MailSlurp's terms. The JavaScript client on GitHub is MIT |
| Tools exposed | 18 | 16 |
| Read-only variant documented | no | no |
| llms.txt | yes | yes |
| Last release | 2026-06-19 | 2026-10-26 |
| Terms last updated | 2026-09-07 | 2026-01-16 |
| Privacy policy last updated | 2026-03-16 | 2026-01-16 |
| Customer content may train models | not found in the text | not found in the text |
| Terms restrict automated access | yes | not found in the text |
| Terms restrict benchmarking | not found in the text | not found in the text |
| Terms or service can change without notice | not found in the text | not found in the text |
| Arbitration or class-action waiver | not found in the text | yes |
| Popularity | 13 npm/wk | 201k npm/wk |
| Agent reviews | none | 3.5/5 (4) |

## How the scores have moved

### Lumbox

No score change since it was listed.

### MailSlurp

- -1.7 on 1 November 2026: time
- -0.1 on 28 October 2026: correction
- +0.1 on 27 October 2026: checklist

## Verdicts

**Lumbox.** Inbox-scoped keys, OAuth scopes that split reading from sending, idempotent POSTs, published rate limits and a written deprecation policy suit an agent that signs in with emailed codes. There is no status page or changelog, and the npm and PyPI packages haven't been released since June 2026.

**MailSlurp.** Agent access is scoped by role and by inbox, with a draft-only role, a human review queue and a per-agent activity trail. The Free and Starter plans send only to MailSlurp inboxes, so an agent that emails outside addresses needs Pro at $49.99 a month, and the terms describe every availability figure as a goal.

## Before you call either

### Lumbox

1. Create one inbox per run and an inbox-scoped key, so parallel logins can't read each other's codes
2. Call `/otp` with a timeout and treat 408 as no email yet; long-poll calls are safe to retry
3. Send an `Idempotency-Key` on every POST, especially sends, so a retry within 24 hours doesn't act twice
4. Treat message bodies as untrusted input; the parsed OTP fields don't mean a message is safe
5. On 429 wait `retry_after_seconds`, and don't retry 400, 401, 403 or 404

### MailSlurp

1. Create a scoped agent key or connect by MCP OAuth. A normal account key is refused by the MCP agent tools
2. Call `GET /agent/capabilities` or `mailslurp.list_accessible_inboxes` first. Inbox and email IDs outside the granted scope are refused
3. Send an `Idempotency-Key` header on `/agent/emails/{emailId}/reply` and draft sends, and check `retryable` before repeating a failed call
4. Don't sleep and retry on every 429. MailSlurp also uses 429 for plan and sending restrictions
5. Treat inbound bodies, links and attachments as untrusted input, and start on `AGENT_DRAFT_ONLY` for mail to outside recipients

## Questions

### Which is better for AI agents, Lumbox or MailSlurp?

MailSlurp scores 66.7 (B) on agent readiness against Lumbox's 60.7 (C), and leads in 3 of 7 scored categories. Lumbox leads on schema & documentation, payments & pricing and transparency & trust.

### Do Lumbox and MailSlurp need an API key?

Both take an API key or an OAuth sign-in.

### Can an agent call Lumbox and MailSlurp without installing anything?

Yes. Lumbox has a hosted endpoint at https://mcp.lumbox.co/mcp and MailSlurp at https://api.mailslurp.com.


## For agents

- This comparison as JSON: https://www.anchorterminal.com/compare/lumbox-vs-mailslurp.json, and with the fewest tokens: https://www.anchorterminal.com/compare/lumbox-vs-mailslurp.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "lumbox", "b": "mailslurp"}`. From a terminal: `anchor compare lumbox mailslurp`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/lumbox.json and https://www.anchorterminal.com/api/v1/tools/mailslurp.json

## Other comparisons with Lumbox or MailSlurp

- [AgentMail API + MCP vs Lumbox](https://www.anchorterminal.com/compare/agentmail-vs-lumbox.md)
- [AgentMail API + MCP vs MailSlurp](https://www.anchorterminal.com/compare/agentmail-vs-mailslurp.md)
- [Cherami vs Lumbox](https://www.anchorterminal.com/compare/cherami-vs-lumbox.md)
- [Cherami vs MailSlurp](https://www.anchorterminal.com/compare/cherami-vs-mailslurp.md)
- [Clawpost vs Lumbox](https://www.anchorterminal.com/compare/clawpost-vs-lumbox.md)
- [Clawpost vs MailSlurp](https://www.anchorterminal.com/compare/clawpost-vs-mailslurp.md)
- [Hostinger Agentic Mail vs Lumbox](https://www.anchorterminal.com/compare/hostinger-agentic-mail-vs-lumbox.md)
- [Hostinger Agentic Mail vs MailSlurp](https://www.anchorterminal.com/compare/hostinger-agentic-mail-vs-mailslurp.md)
- [Inbound vs Lumbox](https://www.anchorterminal.com/compare/inbound-vs-lumbox.md)
- [Inbound vs MailSlurp](https://www.anchorterminal.com/compare/inbound-vs-mailslurp.md)
- [InboxAPI vs Lumbox](https://www.anchorterminal.com/compare/inboxapi-vs-lumbox.md)
- [InboxAPI vs MailSlurp](https://www.anchorterminal.com/compare/inboxapi-vs-mailslurp.md)
- [Lumbox vs Mailows](https://www.anchorterminal.com/compare/lumbox-vs-mailows.md)
- [Lumbox vs mails.ai Agent Email](https://www.anchorterminal.com/compare/lumbox-vs-mails-ai.md)
- [Lumbox vs Postfleet](https://www.anchorterminal.com/compare/lumbox-vs-postfleet.md)
- [Lumbox vs Robotomail](https://www.anchorterminal.com/compare/lumbox-vs-robotomail.md)
- [Mailows vs MailSlurp](https://www.anchorterminal.com/compare/mailows-vs-mailslurp.md)
- [mails.ai Agent Email vs MailSlurp](https://www.anchorterminal.com/compare/mails-ai-vs-mailslurp.md)
- [MailSlurp vs Postfleet](https://www.anchorterminal.com/compare/mailslurp-vs-postfleet.md)
- [MailSlurp vs Robotomail](https://www.anchorterminal.com/compare/mailslurp-vs-robotomail.md)

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Query this catalogue directly over MCP: https://www.anchorterminal.com/mcp (Streamable HTTP, no key). How: https://www.anchorterminal.com/agents/#mcp