Send mail in Gmail with python

Question

I'm trying to send a simple test email using the Gmail API but I keep getting the same error for every code sample I find.

My code at the moment is this:

def validationService():
    SCOPES = ['https://mail.google.com/']
    SERVICE_ACCOUNT_FILE = 'creds.json'
    creds = service_account.Credentials.from_service_account_file(SERVICE_ACCOUNT_FILE, scopes=SCOPES)

    service = build('gmail', 'v1', credentials=creds)
    return service


def SendMessage(service, user_id, message):
  try:
    message = (service.users().messages().send(userId=user_id, body=message).execute())
    print('Message Id:',message['id'])
    return message
  except errors.HttpError as error:
    print('An error occurred:', error)


def CreateMessage(sender, to, subject, message_text):
  message = MIMEText(message_text)
  message['to'] = to
  message['from'] = sender
  message['subject'] = subject
  return {'raw': base64.urlsafe_b64encode(message.as_string().encode()).decode()}

service = validationService()

email = CreateMessage("[email protected]", "[email protected]", "Test", "This is a test")

sent = SendMessage(service, "[email protected]", email)

Returns

>>> An error occurred: <HttpError 400 when requesting https://www.googleapis.com/gmail/v1/users/me/messages/send?alt=json returned "Bad Request">

I also don't understand the difference between the "sender" parameter at CreateMessage and userId at SendMessage.

If serves a purpose, I'm using a Service Account credential

- Thanks!

Answer 1

When using a service account with the Gmail API. You need to set domain-wide delegation, which allows the service account to impersonate any user in your G Suite domain. Therefore, you must have a G Suite Account to be able to use domain wide-delegation as the docs say:

If you have a G Suite domain—if you use G Suite, for example—an administrator of the G Suite domain can authorize an application to access user data on behalf of users in the G Suite domain.

So now, why do you need to impersonate a user(a real person)? it's due to the fact a service account is a bot(not a real person) that is used to server-to-server interactions making possible your app calls Google APIs and although the service account has a parameter called client_email, which has a structure like [email protected] it's not a real email that belongs to a real person (kind of confusing I know).

Having said that, I made some changes to your code. First, I modified your validationService function in order to build the service using domain-wide delegation.

def validationService():
    # Set the crendentials 
    credentials = service_account.Credentials.\
        from_service_account_file(SERVICE_ACCOUNT_FILE, scopes= SCOPES)
    # Delegate the credentials to the user you want to impersonate
    delegated_credentials = credentials.with_subject(USER_EMAIL)
    service = discovery.build('gmail', 'v1', credentials=delegated_credentials)
    return service

In your SendMessage function is not necessarily to pass the user who is going to send the email. Using me is enough as the Users.messages: send Parameters state:

userId string The user's email address. The special value me can be used to indicate the authenticated user.

def SendMessage(service, message):
    message = service.users().messages().send(userId="me", body=message).execute()
    return message

Your whole code at the end could look like this one:

from googleapiclient import discovery, errors
from oauth2client import file, client, tools
from google.oauth2 import service_account
from email.mime.text import MIMEText
import base64

SERVICE_ACCOUNT_FILE = 'service_account.json'
SCOPES = [' https://mail.google.com/']
# The user we want to "impersonate"
USER_EMAIL = "user@domain"


def validationService():
    # Set the crendentials 
    credentials = service_account.Credentials.\
        from_service_account_file(SERVICE_ACCOUNT_FILE, scopes= SCOPES)
    # Delegate the credentials to the user you want to impersonate
    delegated_credentials = credentials.with_subject(USER_EMAIL)
    service = discovery.build('gmail', 'v1', credentials=delegated_credentials)
    return service


def SendMessage(service, message):
    message = service.users().messages().send(userId="me", body=message).execute()
    return message


def CreateMessage(sender, to, subject, message_text):
  message = MIMEText(message_text)
  message['to'] = to
  message['from'] = sender
  message['subject'] = subject
  return {'raw': base64.urlsafe_b64encode(message.as_string().encode()).decode()}


def main():
    try:
        service = validationService()
        email = CreateMessage(USER_EMAIL, "receiverrmail@domain", "Test", "This is a test")
        email_sent = SendMessage(service, email)
        print('Message Id:', email_sent['id'])
    except errors.HttpError as err:
        print('\n---------------You have the following error-------------')
        print(err)
        print('---------------You have the following error-------------\n')


if __name__ == '__main__':
    main()

Notice

You also need to allow your service account to access Google's API when using domain-wide delegation by setting the Managing API client access on your G Suite account.