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Python email SDK

The Python email SDK: create addresses, receive mail, reply.

Receive email in Python without running a mail server. Create an address in one call, wait for the message that lands on it, read the text, HTML and attachments, and reply in the same thread. Mail arrives encrypted and is opened by your Python process, not by us.

Install the Python package
pip install mailcycle
Create a free accountRead the Python guide

mailcycle on PyPI · Python 3.10 or later · Apache 2.0 · Free tier, no card

Quickstart

Receive and send email in Python.

Sign in, create an address, wait for a message and answer it. That is the whole loop, and it is the same loop whether the mail is a sign-up code, a customer or a receipt.

  1. 1Install mailcycle and set MAILCYCLE_PHRASE to your account's recovery phrase.
  2. 2Create an address with mc.addresses.create(). It receives mail straight away.
  3. 3Wait for the next message with mc.messages.wait_for(), or take it from a webhook.
  4. 4Reply with mc.messages.send(), threaded under the original.
The full Python guide
Python: create an address, wait for mail, reply
import os
from mailcycle import Mailcycle

mc = Mailcycle.sign_in(os.environ["MAILCYCLE_PHRASE"])

# A new address that receives mail, sealed to your key.
address = mc.addresses.create(prefix="signup", label="Test run 42")
print(address.email_address)  # signup-x7k2@...

# Wait for the verification email, decrypted here.
message = mc.messages.wait_for(
    address_id=address.id, subject="verification", timeout=60
)
print(message.subject, message.text)

# Reply in the same thread.
mc.messages.send(
    from_address=address.email_address,
    to=message.reply_to,
    subject=f"Re: {message.subject}",
    text="Thanks, confirmed.",
    reply_to=message,
)
What it does

The whole email API, from Python.

Everything the Mailcycle console can do is in the package: addresses, inbound mail, sending, webhooks, events, API keys and devices.

Create email addresses from Python

mc.addresses.create() mints a new address on a shared domain, or on your own domain from Scale, and it receives mail at once. Give it a prefix and a label sealed on your machine.

Receive email and wait for it

mc.messages.wait_for() listens on the event stream and returns the next matching message, filtered by sender or subject, opened and ready to read. Without a stream it checks every five seconds.

Read and parse incoming email

mc.messages.list() and .attachment() return the sender, subject, plain text, the original HTML, a safe HTML with remote images and trackers removed, and every attachment as bytes.

Send email and reply in the thread

mc.messages.send() sends from an address your account owns, with up to ten files. Pass the message you are answering and the threading headers are filled in.

Inbound email webhooks

Register a URL and every message.received event is POSTed to it, signed with HMAC-SHA256 and retried. verify_webhook_signature() checks the signature in one line.

A live event stream

mc.events.stream() carries the same events over a WebSocket the moment they happen, and reconnects after a drop. Events carry ids, never content.

Email testing

Test email verification in pytest, Playwright for Python and Selenium.

Create a fresh address in a pytest fixture, drive your sign-up form with Playwright or Selenium, then call wait_for and pull the one-time code or magic link out of message.text. Delete the address in teardown and its place on your plan is free again.

  • A real address on a real domain, so the mail goes through the same path your users' does.
  • One call blocks until the message lands, filtered by subject or sender, with a timeout you set.
  • Text, HTML and attachments come back parsed, so pulling out a code or a link is a regular expression.
  • Mail received from the moment you start waiting counts, even if it lands before the stream is up.
Inbound email webhooks

Handle incoming email in Flask, Django and FastAPI.

Rather than polling, let the mail come to you. A webhook POSTs each event to your URL the moment it happens, signed so you can prove it came from Mailcycle, and retried if your server is down.

Events carry ids, never content. Fetch the message by id and it is opened in your code, exactly as it would be otherwise. Webhooks are on Operator and above.

Webhooks in the docs
Flask: verify a webhook, then fetch the message
from flask import Flask, abort, request
from mailcycle import verify_webhook_signature

app = Flask(__name__)

@app.post("/hooks/mailcycle")
def mailcycle_webhook():
    raw = request.get_data()  # the body exactly as it arrived
    signature = request.headers.get("Mailcycle-Signature")
    if not verify_webhook_signature(SECRET, raw, signature):
        abort(401)

    event = request.get_json()
    if event["type"] == "message.received":
        message = mc.messages.get(event["payload"]["messageId"])
        handle(message.subject, message.text)
    return "", 204
No mail server

Instead of smtplib, imaplib and a mailbox.

Python's standard library can speak SMTP and IMAP, but smtplib needs an SMTP server to hand mail to and imaplib needs a mailbox to read from. You end up provisioning a mail account, storing its password, polling it and parsing raw MIME with the email package.

Here an address is a function call, mail is pushed to a webhook or waited on with one blocking call, and the message comes back already parsed: sender, subject, text, HTML with remote content stripped, and attachments as bytes.

It is not a bulk sender. If you need newsletters or high volumes of transactional mail, use a sending service for that; Mailcycle is for addresses your code owns and the mail that comes back to them.

End-to-end encrypted

Mail is opened in your Python code, not on our servers.

Each address has a key pair derived from your recovery phrase. Incoming mail is sealed to its public key before anything is written down, and the package derives the private key on your machine to open it.

How the encryption works
  • Signing in proves you hold the key by answering a challenge, so the phrase never crosses the wire.
  • Bodies, attachments, address labels and API key names are all sealed. The server stores ciphertext.
  • Mail sealed by one SDK opens in every other, and in the app, because they share one published format.
  • The package is checked against Mailcycle's published test vectors, including the cases that must be refused.
  • Because the server cannot read mail, there is no server-side search. Search runs where the mail is opened.
Use cases

What developers build with the Python SDK.

It runs in Django and Flask apps, FastAPI services, Celery workers, Jupyter notebooks and command-line scripts: anywhere Python code needs an email address of its own.

End-to-end tests for sign-up and login

Verification emails, one-time passcodes, magic links, password resets and invitations, checked by a real test in pytest, Playwright for Python and Selenium.

A support or orders inbox your code answers

Give an address to a queue, read what customers send, and reply from the address they wrote to, threaded under their message.

Receipts, invoices and alerts as data

Point suppliers, monitoring and other services at an address and pull the text and attachments straight into your own records.

An address per customer, job or device

Mint addresses on demand and keep each stream of mail separate, with its own label, and delete one when the job is done.

Building an AI agent? It can have an inbox too, through the Mailcycle MCP server, without writing any Python at all.

The package

Python SDK at a glance.

Maintained by Mailcycle, the team that runs the API.

The Mailcycle Python SDK at a glance
Packagemailcycle
RegistryPyPI
Install withpip, uv or Poetry
NeedsPython 3.10 or later
AlsoAdd the events extra, pip install 'mailcycle[events]', for the live event stream.
LicenceApache 2.0, free to use in your own applications
APIJSON over HTTPS at api.mailcycle.email
GuideThe Python guide in the docs

What each plan unlocks. Free receives mail. A signed-in session sends from Personal up. API keys and webhooks start at Operator, and sending from an API key at Scale. See pricing.

Questions

Python email SDK questions.

Install the package with pip install mailcycle, sign in with your recovery phrase, and create an address with mc.addresses.create(). Mail sent to that address is stored encrypted, and mc.messages.list() or mc.messages.wait_for() returns it decrypted, with the sender, subject, text, HTML and attachments already parsed. There is no mail server or IMAP account to set up.

Call mc.messages.send() with a from address your account owns, a recipient, a subject and text. The API sends it; you never configure SMTP credentials. Passing reply_to=message fills in the threading headers so the reply lands in the same conversation. Sending from a signed-in session works from the Personal plan, and from an API key on Scale and above.

Yes. Create an address in a fixture, submit it to the sign-up form under test, and call mc.messages.wait_for(address_id=..., subject=...) to block until the verification email arrives, then read the code or link from message.text. If nothing arrives before the timeout it raises an APIError with the code timeout, which fails the test cleanly.

Python 3.10 or later. The live event stream needs the optional websockets dependency, installed with pip install 'mailcycle[events]'. Without it, wait_for checks the address every five seconds instead.

The package is free and open source under the Apache 2.0 licence. The Mailcycle Free plan costs nothing and needs no card: 3 email addresses and 3,000 messages received a month, receive only. Sending starts on Personal at $7 a month, API keys and webhooks on Operator at $15, and sending from an API key on Scale at $19.

No. Incoming mail is sealed to the address's public key before it is stored, and the private key is derived from your recovery phrase inside your Python process. The server holds ciphertext it cannot open. Mail you send leaves in plain text so the recipient's server can read it, and the copy kept in Sent is sealed like the rest.

Call mc.addresses.create() at the start of the run and delete the address at the end, which frees its place on your plan. Each address receives mail as soon as it exists. This is for testing your own product and for mail meant for you: registering accounts on other services in bulk, or against their terms, breaks the Acceptable Use Policy.

No. Mailcycle is inbound email infrastructure, and sending is there to answer what arrives. Sending is capped at 60 messages an hour per account and 20 an hour per device or agent, with a daily limit set by the plan, and the Acceptable Use Policy rules out bulk, marketing and outreach mail.

The API is plain JSON over HTTPS at api.mailcycle.email, so anything can call it. Message content comes back encrypted, though, and the package is what derives the keys and opens it. Without an SDK you would implement the published encryption format yourself.
Other languages

The same API in every language you use.

Nine SDKs share one encryption format, so a message created by one opens in all the others.

Give your Python code an email address.

Create an account, create an address, and read what arrives. The free tier needs no card.

Get startedRead the Python guide