mailcapture

Official Python SDK for MailCapture — a real email capture API for integration testing OTP codes, verification links, and other transactional emails.

mailcapture is the Python client for the MailCapture service. Your application sends email to a unique MailCapture address during a test; this library retrieves that email so your test can assert on its contents — subject line, body text, OTP codes, links, and more. Both synchronous and async clients are included.

A MailCapture account is required — free and paid plans are available. Sign up at mailcapture.app.

Installation

pip install mailcapture

Requires Python 3.9+.

Quick start

from mailcapture import MailCapture

with MailCapture(api_key) as mc:
    mc.ping()  # validates key, caches your username

    # Send an email to {username}-signup@mailcapture.app, then:
    email = mc.wait_for("signup", timeout=15)

    print(email.subject)   # "Welcome to Acme!"
    print(email.otp)       # "123456" — extracted automatically

The pattern for integration tests

1. Clear the inbox before each test
2. Trigger the action that sends the email (register, reset password, etc.)
3. Wait for the email — wait_for holds the connection open and returns the instant it arrives
4. Assert on subject, OTP, body, links
5. Clean up after

# pytest example
import pytest
from mailcapture import MailCapture

@pytest.fixture(scope="session")
def mc():
    with MailCapture(os.environ["MAILCAPTURE_API_KEY"]) as client:
        client.ping()
        yield client

def test_signup_otp(mc):
    inbox = mc.inbox("signup")
    inbox.clear()                             # clean starting state

    register_user(inbox.address)              # "alice-signup@mailcapture.app"

    email = inbox.wait_for(timeout=10)

    assert email.subject == "Verify your email"
    assert re.match(r"^\d{6}$", email.otp)

Async usage

import asyncio
from mailcapture import AsyncMailCapture

async def test_signup():
    async with AsyncMailCapture(api_key) as mc:
        await mc.ping()
        inbox = mc.inbox("signup")
        await inbox.clear()

        await register_user(inbox.address)

        email = await inbox.wait_for(timeout=10)
        assert email.otp is not None

API reference

MailCapture(api_key, *, base_url=..., request_timeout=...)

AsyncMailCapture(api_key, *, base_url=..., request_timeout=...)

Both clients accept the same constructor arguments.

Argument	Default	Description
api_key	required	Your mc_... API key
base_url	https://mailcapture.app	Override for local dev
request_timeout	10.0	Default timeout in seconds

Both support context manager usage (with / async with) for clean connection handling.

---

ping() → PingResult

Validates your API key and returns your address template. Also caches your username so address() works synchronously.

result = mc.ping()
print(result.username)          # "alice"
print(result.address_template)  # "alice-{tag}@mailcapture.app"

---

wait_for(tag, *, timeout=30, poll_timeout=10, after=None) → Capture

Long-polls the API and returns the first email captured for the given tag. The server holds the connection open — no busy-waiting.

email = mc.wait_for("signup", timeout=15)

Argument	Default	Description
tag	required	Which inbox to watch
timeout	30	Total wait in seconds
poll_timeout	10	Per-poll server timeout in seconds (max 30)
after	60s ago	Only return captures received after this datetime

Raises MailCaptureTimeoutError if no email arrives in time.

---

inbox(tag) → Inbox / AsyncInbox

Returns a scoped inbox object for a tag. Keeps test code clean.

inbox = mc.inbox("password-reset")

inbox.address          # "alice-password-reset@mailcapture.app" (requires ping() first)
inbox.wait_for(timeout=10)
inbox.list(limit=5)
inbox.clear()

---

address(tag) → str

Generates the capture email address synchronously. Requires ping() first.

mc.ping()
mc.address("signup")  # "alice-signup@mailcapture.app"

---

list(*, tag=None, after=None, limit=None) → CaptureList

List recent captures (newest first).

result = mc.list(tag="signup", limit=10)
for email in result.items:
    print(email.subject)

---

get(capture_id) → Capture

Get a single capture by ID. Raises MailCaptureNotFoundError if not found.

---

delete(tag) → None

Delete all captures for a tag. Use before each test for a clean inbox.

---

The Capture object

@dataclass
class Capture:
    id: str           # UUID
    tag: str          # e.g. "signup"
    subject: str      # email subject line
    otp: str | None   # extracted OTP/code, if detected
    body_text: str | None
    body_html: str | None
    latency_ms: int   # time from send to capture, in ms
    status: str
    received_at: str  # ISO 8601 timestamp

The otp field is extracted automatically. If your OTP is embedded in a sentence, the service finds it for you. None if no code was detected.

---

Error handling

All errors extend MailCaptureError and have a .code attribute.

from mailcapture import (
    MailCaptureAuthError,
    MailCaptureTimeoutError,
    MailCaptureNotFoundError,
    MailCaptureNetworkError,
)

try:
    email = mc.wait_for("signup", timeout=10)
except MailCaptureTimeoutError as e:
    print(f"Waited {e.waited_seconds:.0f}s for tag '{e.tag}' — nothing arrived")
    print("Did the email actually send? Check your email service logs.")
except MailCaptureAuthError:
    print("Check your MAILCAPTURE_API_KEY environment variable.")
except MailCaptureNetworkError:
    print("Could not reach MailCapture. Check your network connection.")

Exception	.code	When
MailCaptureAuthError	UNAUTHORIZED	Invalid or revoked API key
MailCaptureTimeoutError	TIMEOUT	wait_for exceeded its timeout
MailCaptureNotFoundError	NOT_FOUND	get(id) — capture not found
MailCaptureNetworkError	NETWORK_ERROR	Could not reach the API
MailCaptureApiError	varies	Unexpected API error

---

Parallel tests

Each tag is its own inbox — safe to run concurrently.

import asyncio
from mailcapture import AsyncMailCapture

async def test_parallel():
    async with AsyncMailCapture(api_key) as mc:
        await mc.ping()

        signup = mc.inbox("signup")
        reset  = mc.inbox("password-reset")

        await asyncio.gather(signup.clear(), reset.clear())

        # Trigger both emails...

        signup_email, reset_email = await asyncio.gather(
            signup.wait_for(timeout=15),
            reset.wait_for(timeout=15),
        )

---

Local development

mc = MailCapture(api_key, base_url="http://localhost:3002")

---

Environment variable

The SDK does not read environment variables automatically. Pass your key explicitly:

import os
mc = MailCapture(os.environ["MAILCAPTURE_API_KEY"])

Get your API key at mailcapture.app/admin/api-keys.