Disposable Address API: Create and Rotate Inbox IDs

When you build AI agents, automated QA, or high-volume signup and verification flows, email becomes a bottleneck fast. Traditional inboxes are hard to isolate per task, hard to reset between runs, and messy to parse reliably. A disposable address API flips that: each workflow gets its own inbox identifier (inbox ID), you rotate it whenever you want, and your app receives emails as structured data instead of scraping HTML.

This article explains how a disposable address API typically works, how to create and rotate inbox IDs safely, and what to look for if you’re wiring it into LLM agents or automation.

What “create and rotate inbox IDs” really means

A disposable inbox system usually has three concepts:

• Inbox ID: a unique identifier you generate (or the provider generates) to represent a mailbox.
• Email address: derived from the inbox ID plus a domain (shared domain or your custom domain). Incoming mail routes to that inbox.
• Message retrieval: you fetch messages (polling) or receive them (webhook) as JSON.

“Rotate” means you stop using one inbox ID and switch to a fresh one, either per run, per user, per attempt, or on a schedule. Rotation gives you isolation and makes cleanup simple: instead of deleting threads from a shared mailbox, you just abandon the ID.

For AI agents, this matters because the agent often needs a clean, deterministic channel for one job (for example, “sign up, confirm email, extract code, proceed”), without being confused by older messages.

When a disposable address API is the right tool (and when it’s not)

A disposable address API is ideal when:

• You need many inboxes (hundreds to millions) for parallel workflows.
• You need machine-readable email (JSON) to drive automation.
• You need fast reset and isolation between runs.
• You need inbound email as an event (webhooks) so agents can react in near real time.

It’s less ideal when:

• You need a long-lived mailbox with human collaboration features.
• You need sending, threaded conversations, or full “mail client” functionality.

For verification flows and QA, rotating disposable inbox IDs is typically the simplest reliable pattern.

Core capabilities to expect from a disposable address API

If you’re designing against (or selecting) a provider, these capabilities determine how well rotation will work in production.

Inbox lifecycle controls

You’ll usually want:

• Create inbox
• List messages for inbox
• Get message by ID
• Optional delete or expire inbox

Even if your provider doesn’t support explicit deletion, rotation still works as long as old inboxes become irrelevant (and ideally expire).

JSON output that is automation-friendly

Email is notoriously messy. A provider that normalizes into structured JSON reduces brittle parsing.

At a minimum, useful fields include:

• From, to, subject, date
• Text body and HTML body
• Headers
• Attachments metadata (if supported)

For standards background on email headers and formatting, RFC 5322 is the canonical reference: RFC 5322.

Webhooks or polling (preferably both)

Webhooks reduce latency and wasted polling. Polling can be a fallback for firewalled environments or retries.

Mailhook, for example, supports both real-time webhook notifications and a polling API, which makes it easier to build robust “wait for email” steps in agents and test runners.

Reference architecture: agent-friendly disposable inboxes

A common architecture for LLM agents and QA runners looks like this:

1. Your orchestrator creates an inbox ID via API.
2. It hands the derived email address to the target site’s signup or verification flow.
3. When the email arrives, your system receives a webhook (or polls).
4. Your automation extracts the verification link or code from the JSON.
5. The run completes and the inbox ID is rotated out.

Rotation strategies (choose based on failure modes)

Rotation is not one-size-fits-all. The right strategy depends on how you debug, how you handle retries, and whether multiple systems can send mail to the same address.

Rotation strategy	Best for	How it works	Main risk	Mitigation
Per run (ephemeral)	QA, CI, load tests	New inbox ID every test run	Harder to inspect after failure if inbox expires quickly	Store message JSON in your logs or test artifacts
Per user session	Multi-step onboarding	One inbox for the whole session	Cross-contamination if sessions collide	Use strong unique IDs, enforce uniqueness in your DB
Per attempt (retry-safe)	Flaky email delivery	New inbox each retry attempt	More inboxes created	Apply TTLs and cleanup policies
Time-boxed (rotating window)	Long-running agents	Rotate every N minutes/hours	Late emails might arrive to old inbox	Keep a grace window and monitor both inboxes

For most agent workflows, per attempt is the most reliable, because it avoids ambiguity when a user or system retries a signup.

A practical “create and rotate” data model

Treat inbox IDs like short-lived credentials. Your system should track them explicitly.

A simple table (or document) usually needs:

• inbox_id
• email_address
• purpose (for example, signup_verification, password_reset, receipt_ingestion)
• run_id or trace_id
• status (active, rotated, expired)
• created_at, rotated_at

This model makes it easy to answer questions like “Which inbox was used for this test run?” and “Should we still accept messages for this inbox?”

Example flow (API-agnostic) for creating an inbox ID

Providers differ on exact routes and authentication, but the logic stays consistent.

1) Create an inbox

Use your provider’s “create inbox” endpoint and store the returned identifier.

{
  "inbox_id": "inbx_7f3c2a...",
  "address": "[email protected]",
  "created_at": "2026-01-15T15:16:53Z"
}

2) Use the address in your workflow

Pass address to the target system (signup form, OAuth test user flow, B2B invite, etc.).

3) Wait for email (webhook-first, polling fallback)

A robust pattern is:

• Subscribe to webhooks for near real-time delivery.
• Also allow polling as a fallback in case webhook delivery fails temporarily.

Method	Latency	Operational complexity	Failure modes	Best practice
Webhook	Low	Medium (needs endpoint, retries)	Endpoint downtime, signature verification failures	Verify signatures, implement idempotency, return 2xx fast
Polling	Medium to high	Low to medium	Rate limits, wasted requests, slower tests	Exponential backoff, stop after timeout

Mailhook supports signed payloads for security, which is exactly what you want for webhook verification.

Extracting what the agent needs (without brittle parsing)

Most verification emails boil down to one of these:

• A link (magic link, confirm email, reset password)
• A numeric or alphanumeric code (OTP)

If your provider returns both text and html, prefer parsing the text first. HTML parsing is more error-prone, especially with tracking wrappers.

A practical extraction approach for agents:

• Prefer a dedicated field if the provider offers link extraction.
• Otherwise, scan the text for URLs and select by domain allowlist.
• For codes, use patterns constrained by expected length and nearby keywords (for example, “Your code is”).

Keep the extracted artifact and the raw message JSON together in your run logs. This is invaluable when a site changes its email template.

How to rotate inbox IDs safely

Rotation is easy to implement poorly. The goal is to avoid:

• Accepting late emails into the “wrong” run
• Losing messages during retries
• Creating race conditions when multiple workers share state

Use explicit states and a grace window

A solid approach is:

• Mark an inbox as active when created.
• When you rotate, mark it rotated but keep it readable for a short grace window (for example, 10 to 30 minutes).
• After the grace window, mark it expired and stop listening.

This helps with late deliveries while still keeping your system clean.

Make “wait for email” idempotent

If you use webhooks, the same message can be delivered more than once due to retries. Your handler should be idempotent.

Typical idempotency key choices:

• Provider message ID
• Hash of (inbox_id + subject + date + from)

Store processed message IDs so your agent does not double-click verification links.

Rotate on failure, not just on time

In signup verification, the most common reason to rotate is not time passing, it’s ambiguity:

• The user retries signup.
• The test runner reruns a failed test.
• The target system sends multiple verification emails.

Rotating per attempt keeps each inbox tied to a single “expected email,” which simplifies the agent’s reasoning.

Domains: shared domains vs custom domain

Many disposable inbox providers offer instant shared domains, and some support custom domains.

Shared domains are convenient for testing and internal tooling, but custom domains can matter when:

• The site under test blocks known disposable domains.
• You need brand consistency for client-facing operations.
• You want stricter control over deliverability reputation.

If you are building production verification flows (not just QA), custom domain support is often worth it.

Security and compliance basics (don’t skip this)

Email can carry sensitive data (login links, invoices, PII). If you are routing it through automation, treat inbox IDs as secrets.

Key practices:

• Verify webhook signatures for every event (Mailhook supports signed payloads).
• Restrict access to message retrieval endpoints with least privilege.
• Encrypt stored message data if you persist email JSON.
• Redact secrets in logs (verification links often include tokens).
• Set retention policies (keep only what you need for debugging and compliance).

For webhook signature verification patterns, Stripe’s webhook docs are a widely referenced example of best practices: Stripe: verifying webhooks.

QA automation: a clean pattern for test suites

If your goal is CI stability, the disposable inbox pattern should minimize flakiness:

• Generate inbox per test case (or per test class if the suite is huge).
• Wait for email with a bounded timeout.
• If timeout occurs, rotate and retry once (and attach raw message logs to the failure).

Avoid running many tests against the same inbox. Shared inboxes create nondeterminism, which is the enemy of reliable CI.

LLM agents: making email a tool, not a distraction

Agents perform best when tools are deterministic. An inbox that returns structured JSON is a good tool interface, because it reduces “interpretation” work.

If you’re building an agent tool spec, define:

• create_inbox(purpose, run_id) -> {inbox_id, address}
• wait_for_message(inbox_id, timeout_s) -> {message_json}
• rotate_inbox(inbox_id) -> {new_inbox_id, new_address}

Keep the agent out of infrastructure details (like backoff logic, webhook retries, signature verification). Let your orchestrator handle that, and expose clean primitives.

Where Mailhook fits

Mailhook is built specifically for programmable disposable inboxes: you can create inboxes via API, receive emails as structured JSON, and integrate via webhooks or polling. If you need a disposable address API that plays nicely with AI agents and automated workflows, it’s a direct match for this “create and rotate inbox IDs” pattern.

You can explore the product at Mailhook.