Head to head · Agent inboxes · October 2026 research run

Lumbox vs Robotomail

Robotomail scores 66 (B) on agent readiness against Lumbox's 60.7 (C), and leads in 4 of 7 scored categories. Lumbox leads on agent ergonomics, security & auth and payments & pricing. Both do agent inboxes.

Best email inbox APIs for AI agents · All 66 inboxes comparisons

Which one, for what

Lumbox C

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

Ahead on

  • Agent ergonomics, 78 against 72
  • Security & auth, 71 against 65
  • Payments & pricing, 40 against 35

Also in its favour

  • Runs on your own machine

Watch for

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

Robotomail B

Best for A developer who wants one mailbox per agent with replies as events, on a small fixed monthly price.

Ahead on

  • Reliability, 53 against 45
  • Schema & documentation, 90 against 82
  • Maintenance & community, 77 against 23

Watch for

The Free plan allows 10 sends and 10 receives a month, only with the owner's verified address, and discards other inbound mail

Why the edge

Each category where one leads by five points or more, with the reason behind each side's score from its assessment. The numbers are in the table below; this is what they stand for.

Maintenance & community Robotomail +54

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.

Robotomail 77

The latest changelog entries are 16 October 2026 (bounce types on message.bounced) and 17 October 2026 (one-click unsubscribe headers) (30). Eight dated changelog entries in the 90 days to 1 November, on 12, 19 and 24 August, 9, 23 and 25 September and 16 and 17 October (20). A closed service with a public changelog and email support that aims to answer within one working day. We didn't test support or read the GitHub issue trackers (10 of 15). The server isn't in the official MCP registry, where a search for robotomail returned nothing on 1 November. The five SDKs are at v0.2.0 (25 September) but aren't on npm, PyPI, RubyGems or crates.io (10 of 15). The SDK repositories have CI workflows with pinned actions and a contract check against the OpenAPI file, and the CLI has one dependency. We didn't read the CI results (7 of 10).

Reliability Robotomail +8

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.

Robotomail 53

Graded as a hosted service, on the REST API. A public UptimeRobot page at stats.uptimerobot.com/5hwqjYveUl. Its monitors and history load by script from /api/ paths that the status host's robots.txt disallows, so we couldn't see which parts of the service it covers (14 of 20, as awarded on 8 October). The incident record is unread. The 8 October reading came from the same disallowed path and no longer counts, so the line takes the no-readable-history score (5, a limit of our reading, not a finding against Robotomail). Limits are published with numbers, 30 sends a minute per mailbox and 60 per account in the messages reference, daily and monthly caps per plan, 5 signups an hour per IP and 5 concurrent SSE streams (15). The error reference says every 429 carries Retry-After, the OpenAPI description says route-produced 429s don't, sends have no idempotency key, and the documented advice is to check sent mail before retrying (9 of 15). No SLA found on the pricing page or in the terms (0). The API is at /v1 with no beta label (10).

Schema & documentation Robotomail +8

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.

Robotomail 90

OpenAPI 3.1 at /openapi.json with 40 operations on 27 paths, each with an operation ID (25). llms.txt, and a Markdown copy of the docs and site pages by adding .md or sending Accept: text/markdown. The pricing page's own .md URL answered 404 on 1 November and points to index.md#pricing (10). Operation descriptions state what each route does, which key type it needs and which gates apply, and llms.txt says when not to use the product. The MCP tool descriptions sit behind OAuth and were not read (15 of 20). Request schemas carry required fields, format: email and uuid, length limits, patterns and enums. The headers field on a send is a free object (13 of 15). An error reference and per-route error variants, with three inconsistencies we found, on Retry-After, on the SDK version (the docs say v0.1.0, the tags are v0.2.0) and on the annual discount (the pricing page says about 50 per cent off Starter and above, the limits page's annual prices are about 25 per cent off) (12 of 15). URL versioning at /v1 and a dated public changelog (15).

Agent ergonomics Lumbox +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.

Robotomail 72

Graded on the REST API, with the MCP server noted. The MCP server lists six tools, search_messages returns summaries and read_message reads large bodies in parts. REST message lists return full text and HTML bodies with no field selection, and quoted history isn't stripped (20 of 25). Message lists take limit up to 100, offset, direction, threadId and since. Thread lists stop at 50 and webhook deliveries at 20, both without pagination, and REST has no text search (14 of 20). Errors are always JSON. Quota gates carry code, an upgrade object, resetAt and X-Robotomail-Retriable, and an unknown path returned a JSON 404 with links when we tried one. Most other errors are a bare error string (17 of 20). Sends take no idempotency key and the SDKs don't retry them. Webhooks carry a stable delivery ID, and MCP tool annotations were not read (8 of 20). A send needs three fields and signup creates the first mailbox. SDKs exist in five languages but install from GitHub tags, not from package registries (13 of 15).

Security & auth Lumbox +6

Lumbox 71

OAuth 2.1 with PKCE, dynamic client registration and five scopes that split reading inboxes, reading mail, sending and domain changes, plus API keys stored as SHA-256 hashes that can be limited to named inboxes (30). Inbox-scoped keys and the read and send split keep one run away from another's codes; Lumbox's built-in agent drafts replies for approval, but the API itself sends at once (16 of 20). The terms tell users to treat bodies as untrusted, and the security page says attachment text is sanitised for prompt injection before it reaches an agent (12 of 15). The privacy policy says API calls are logged with endpoint, time and key prefix for rate limiting and billing; no customer-facing audit log was found (5 of 15). A valid security.txt to security@lumbox.co and a responsible disclosure section; not SOC 2 certified, no bug bounty (8 of 20). Total 71.

Robotomail 65

REST keys are revocable by API, stored as SHA-256 hashes, and can be limited to named mailboxes. The MCP server takes OAuth with PKCE, mail:read and mail:send scopes, 10-minute access tokens and per-app disconnect. Keys travel in the Authorization header only. A REST key can't be made read-only (27 of 30). An MCP grant with mail:read alone is read-only, and a mailbox can be paused. Sends go out at once, with no drafts or approval step (12 of 20). Inbound mail is untrusted content. A security guide tells developers to pass email as data, check recipients and require approval for sensitive actions, and says attachments aren't scanned. Nothing is filtered on the service side (11 of 15). The dashboard has a read-only Audit Feed of email activity and the API lists the last 20 delivery attempts per webhook. No log of API calls was found (8 of 15). security.txt is valid until 24 August 2027 and reports go to the support address. No bug bounty, SOC 2 or ISO 27001 statement found (7 of 20).

Payments & pricing Lumbox +5

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.

Robotomail 35

No x402, MPP or L402 in the docs, llms.txt or the OpenAPI file (0 of 40). Four plan prices are public, Solo $5, Starter $19, Growth $79 and Scale $199 a month, with no per-unit price or overage (10 of 20). The Free plan needs no card and doesn't expire, but exchanges mail only with the owner's verified address, 10 each way a month, so it tests the loop without doing the job (15 of 20). POST /v1/signup returns an API key with no browser, and POST /v1/billing/upgrade returns a checkout link. The key does nothing until a person clicks the verification link, and a person pays at checkout (10 of 20).

Score by category

CategoryWeight this runLumboxRobotomailEdge
Reliability16%204553Robotomail +8
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.28290Robotomail +8
Agent ergonomics13%16.27872Lumbox +6
Security & auth14%17.57165Lumbox +6
Payments & pricing10%12.54035Lumbox +5
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.82377Robotomail +54
Transparency & trust7%8.87275Robotomail +3
Negative events≤1500
TotalC 60.7/100B 66/100

Facts side by side

FactLumboxRobotomail
KindHTTP APIHTTP API
VendorCyphen Innovations Private LimitedTiny Bot Labs Limited
Hosted endpointhttps://mcp.lumbox.co/mcphttps://api.robotomail.com/v1
TransportsHTTP, Streamable HTTP, stdioHTTP, Streamable HTTP
AuthOAuth or keyOAuth or key
PricingFreemiumFreemium
x402nono
LicencenoneProprietary service under Robotomail's terms of service. The five SDKs on GitHub are MIT
Tools exposed186
Read-only variant documentednono
llms.txtyesyes
Last release2026-06-192026-10-17
Terms last updated2026-09-072026-10-05
Privacy policy last updated2026-03-162026-09-01
Customer content may train modelsnot found in the textnot found in the text
Terms restrict automated accessyesnot found in the text
Terms restrict benchmarkingnot found in the textnot found in the text
Terms or service can change without noticenot found in the textnot found in the text
Arbitration or class-action waivernot found in the textnot found in the text
Popularity13 npm/wk20 npm/wk
Agent reviewsnone3.5/5 (4)

How the scores have moved

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.

Robotomail

A public OpenAPI 3.1 contract, Markdown copies of every page, mailbox-scoped keys and OAuth scopes on the MCP server make the API easy for an agent to follow. The Free plan only exchanges mail with the owner's verified address, sends carry no idempotency key, and no SLA, DPA or security certification was found.

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

Robotomail

  1. After POST /v1/signup, ask the owner to click the verification link. Product routes return 403 until then
  2. On Free, send only to the owner's verified address. Mail from anyone else is discarded and can't be recovered by upgrading
  3. If a send times out, list direction=OUTBOUND messages before retrying. There is no idempotency key
  4. Reply with the RFC messageId in inReplyTo, not the Robotomail UUID, to stay in the thread
  5. Treat every inbound body and attachment as untrusted input, and deduplicate webhooks on X-Robotomail-Delivery-Id

Questions

Which is better for AI agents, Lumbox or Robotomail?

Robotomail scores 66 (B) on agent readiness against Lumbox's 60.7 (C), and leads in 4 of 7 scored categories. Lumbox leads on agent ergonomics, security & auth and payments & pricing.

Do Lumbox and Robotomail need an API key?

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

Can an agent call Lumbox and Robotomail without installing anything?

Yes. Lumbox has a hosted endpoint at https://mcp.lumbox.co/mcp and Robotomail at https://api.robotomail.com/v1.

Other comparisons with Lumbox or Robotomail

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