Receiving mail with the Mail API

This guide describes how to use the Mail API to receive mail.

Email messages sent to your app are implemented as HTTP requests containing MIME data. To process incoming email messages, you associate email addresses with script handlers in your app configuration, then include the handlers in your app's code.

Incoming email generates HTTP requests, which are passed to the appropriate scripts. The scripts that handle the incoming email must reside in your default service.

For more information on the Mail service, see the Mail API Overview.

Before you begin

You must register your sender emails as authorized senders. For more information, see who can send email.

Configuring your application to receive email

When you create a new app, incoming email is disabled by default. To enable the incoming email, you must modify your app.yaml file in your default service.

Add an inbound_services section that enables the incoming email service. For example:
```
inbound_services:
- mail
```
If you don't enable incoming email by including this section in your configuration file, then incoming email is disabled, and email messages sent to the app are ignored.
Add mappings that associate URL-mapped email addresses with script handlers.

For the default service, the email address for receiving email has the following format:
```
[STRING]@[Google Cloud project ID].appspotmail.com
```
For non-default services, the email address has the following format:
```
[STRING]@[servicename]-dot-[Google Cloud project ID].appspotmail.com
```
Email messages are sent to your app as HTTP POST requests using the following URL, where [ADDRESS] is a full email address, including domain name:
```
/_ah/mail/[ADDRESS]
```
To handle incoming email in your app, map email URLs to handlers in the app.yaml file:
```
- url: /_ah/mail/.+
  script: handle_incoming_email.app
  login: admin
```
In the above example, /_ah/mail/.+ matches all email addressed to the app. If you prefer, you can set up multiple handlers for different email addresses, as in the following example:
```
- url: /_ah/mail/owner@.*your_app_id\.appspotmail\.com
  script: handle_owner.app
  login: admin
- url: /_ah/mail/support@.*your_app_id\.appspotmail\.com
  script: handle_support.app
  login: admin
- url: /_ah/mail/.+
  script: handle_catchall.app
  login: admin
```
URLs of incoming email messages are matched to this list from first to last, so if an email message URL matches more than one pattern, the first matching handler will be the one executed. This allows you to include a "catchall" handler as the last mapping. The handlers run in the default module (or application version).

Handling incoming email

When using Python web frameworks, the InboundEmailMessage constructor takes in the bytes of the HTTP request body. There are multiple ways to create the InboundEmailMessage object in Python. In Flask, request.get_data() gives the request bytes. The InboundEmailMessage object contains the email message. Its bodies() method returns the bodies within the message. If you call bodies() without arguments, it returns an iterator that yields HTML bodies first, then plain text bodies. If you want just HTML or just plain text, you can pass an argument to bodies():

@app.route("/_ah/mail/<path>", methods=["POST"])
def receive_mail(path):
    message = mail.InboundEmailMessage(request.get_data())

    # Do something with the message
    print(
        f"Received greeting for {escape(message.to)} at {escape(message.date)} from {escape(message.sender)}"
    )
    for content_type, payload in message.bodies("text/plain"):
        print(f"Text/plain body: {payload.decode()}")
        break

    return "OK", 200

The InboundEmailMessage object includes attributes to access other message fields:

subject contains the message subject.
sender is the sender's address e.g. "Nobody <nobody@example.com>".
to is a comma-separated list of the message's primary recipients e.g. "Joe <joe@example.com>, Bill <bill@example.com>".
cc contains a comma-separated list of the cc recipients e.g. "Joe <joe@example.com>, Bill <bill@example.com>".
date returns the message date.
attachments is a list of Attachment objects, possibly empty.
original is the complete message, including data not exposed by the other fields such as email headers, as a Python email.message.Message.

Simulating incoming messages with the local development server

Once you set up your app to handle incoming email, you can use the development server console to simulate incoming email messages:

Access the development server as an administrator by going to http://localhost:8080/console and selecting Sign in as administrator.
In the development server, click Inbound Mail in the navigation.
Fill out the form that appears, and click Send Email.

To get the development server running, see the local development server.

Learn more about the migration considerations for Mail API in the Mail handlers guide.