Originally published at lumbox.co
Choose Lumbox when you want an agent-owned inbox with a documented, bounded OTP retrieval endpoint and a paid entry plan starting at $9 per month. Evaluate AgentMail alongside it when its email allowances, platform features or existing integration fit your workflow better, because both products provide inbox infrastructure for agents.
I build Lumbox. This comparison is for startups whose browser agents log into third-party portals for customers, rather than a claim that one email service wins every workload. Pricing and documented capabilities were checked on October 3, 2026. Recheck them when making a purchase.
Compare the task before the feature list
Both products can be relevant when an agent needs its own email address. AgentMail’s quickstart shows creating an inbox and sending mail through its SDK. Lumbox exposes inbox creation, email retrieval and sending through its API and tools, documented in its inbox guide and MCP guide.
For customer portal agents, a new address is only part of the job. Existing accounts may send verification mail to a customer’s original mailbox. Neither a new inbox nor a lower subscription price automatically changes that destination. Decide whether the customer will forward relevant mail, change the account address where supported, or provide an authorized mailbox connection.
Then compare how much code your application needs between receiving that message and resuming the browser. That is the point where Lumbox’s OTP endpoint is worth evaluating directly.
A narrow, sourced comparison
Decision pointLumboxAgentMailAgent-owned inboxesAPI creates inboxesAPI and SDK create inboxesFree inbox allowance3 inboxes3 inboxesFree email allowance500 received and 100 sent per monthPricing lists 3,000 emails per monthFirst paid monthly planStarter: $9, 10 inboxesDeveloper: $20, 10 inboxesEmail allowance on that plan5,000 received and 2,000 sent per monthPricing lists 10,000 emails per monthCustom domainsListed in Starter featuresDeveloper lists 10 custom domainsMCP@lumbox/mcp-server, including get_otpPricing lists an MCP serverBounded OTP retrieval evaluated hereGET /v1/inboxes/:id/otp, up to 120 secondsVerify the current preferred extraction and waiting path in its docs
Lumbox figures come from packages/plans/src/index.ts and the pricing docs. AgentMail figures come from its pricing page. The email allowances are presented with their original definitions; a combined “emails” allowance and separate sent/received limits are not automatically equivalent.
This table deliberately does not mark every untested competitor capability as absent. A missing fact in this review is a question for evaluation, not proof that AgentMail cannot do something. It also does not compare deliverability, uptime or extraction accuracy, because no controlled benchmark was run.
What the Lumbox OTP endpoint does
After provisioning and routing, the client makes one retrieval request. The server waits up to the requested timeout for a recent verification-category message containing parsed codes. It returns code, all_codes, from, subject, expires and email_id, or HTTP 408 if no suitable result is found before the wait ends.
The default timeout is 30 seconds and the maximum is 120. The REST route accepts from and since. Without since, it looks back five minutes. These details are implemented in apps/api/src/routes/inboxes.ts and linked through the API reference.
This removes the need for a repeated polling loop in the client for that retrieval step. The server still polls its database once per second. It also does not configure forwarding, prove sender identity, reserve a code for a particular run or confirm that the portal accepted the value.
If these remaining responsibilities already exist in your application, the endpoint can be a compact fit. If you already have a reliable AgentMail integration that supplies the same workflow outcome, switching needs a stronger reason than a shorter example.
When AgentMail deserves a closer look
AgentMail’s published free email allowance is larger than Lumbox’s listed free allowances. A team testing many messages with only a few inboxes should compare that difference using its actual inbound and outbound traffic. The lowest paid subscription is not necessarily the lowest total cost for every workload.
Its pricing page also lists product features such as threads, labels, SDKs and an MCP server. Inspect the capabilities you actually need and their plan availability. If your team already understands AgentMail’s event and message model, that familiarity has practical value even though it cannot be converted into an invented savings figure.
For procurement requirements, request the relevant evidence directly from each vendor. Do not infer equivalent security assurances from similar feature names or a checkbox in a comparison article.
When Lumbox is a useful candidate
Lumbox fits an evaluation centered on inbound verification mail, especially when the application wants a parsed code from a bounded API call. It also provides send and reply, custom domains and a credential vault. Those features have distinct configuration and authorization requirements; they are not a guarantee that a complete portal login works without integration.
The $9 Starter plan gives a small team a lower subscription entry point than the AgentMail Developer plan observed here. That is a price comparison, not a claim that Lumbox is the cheapest agent email service on the market.
Test with a forwarded message from the portal you care about. Check the received sender, extracted code and classification. The parser is rules based, so template coverage matters more than a generic statement that a product “supports OTP.”
Make the decision with a reproducible pilot
Use the same authorized portal account and message templates for both candidates. Record whether mail arrives, whether your extraction path finds the correct value, and whether the browser reaches the intended authenticated state. Include a timeout and a repeated code request.
Track the integration code you maintain, active inbox count, sent and received volume, and the human steps required to onboard a customer. Keep results separate from hypotheses. A successful demonstration with one template does not establish universal portal coverage.
If your immediate blocker is email-code retrieval, start with Lumbox’s API reference and one test inbox. If AgentMail already meets the requirement with an integration you trust, keeping it can be the reasonable decision.
Kumar
Top comments (1)
The point about verification mail still going to the customer's original mailbox is the part most agent-inbox write-ups skip, good to see it up front.
One thing I'd add for portal agents is where the code goes after
get_otp. If the tool returns it to the model, it ends up in the transcript, traces and any eval logs you keep. OTPs are short-lived so that's usually tolerable, but the same pattern tends to get copied for passwords next. A split that has held up for us: the model asks "fill the code into field X", a local tool fetches and types it, and returns only "filled". The model never sees the value, and a prompt-injected portal page can't talk the agent into reading it back out.The other failure worth a test case: portals that split the OTP across six inputs or auto-advance focus, so one paste lands in the first box only. Do you cover that resume step (typing the code into the page), or leave it to the browser-agent framework?