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Daniel is CTO at rhome GmbH, and Co-Founder at Aqarios GmbH. He holds a M.Sc. in Computer Science from LMU Munich, and has published papers in reinforcement learning and quantum computing. He writes about technical topics in quantum computing and startups.
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# Zoho Mail API example in Python Flask

Since I could not find an example out there, here's a comprehensive and complete example on using the Zoho Mail API with Python Flask.

Some pointers: It was very important to make sure that the top level domains of all API URLs match. In my example, they're all dot eu. How it works is as follows: The application prints a register link that needs to be clicked only once per run. It gets an initial access token and a refresh token. A second thread uses the refresh token every hour to get a new valid access token (since they're only valid for one hour). There is also a Flask route to actually send a HTML generated E-Mail for testing.

Now, a possible improvement could be saving the refresh token to the filesystem to persist restarts. But that is an exercise for the developer.

The project can be found here: https://github.com/instance01/zoho-mail-api-example.

Excerpt with the main functionality:

import json
import time
import requests
import threading

from flask import Flask
from flask import request
from flask import render_template

app = Flask(__name__)

# Configure this.
FROM_EMAIL_ADDR = 'mail@yourdomain.de'
TO_EMAIL_ADDR = 'mail@otherdomain.de'
BASE_OAUTH_API_URL = 'https://accounts.zoho.eu/'
BASE_API_URL = 'https://mail.zoho.eu/api/'

    "access_token": "",
    "refresh_token": "",
    "api_domain": "https://www.zohoapis.eu",
    "token_type": "Bearer",
    "expires_in": 3600,
    "account_id": ""

def req_zoho():
    url = (
    print('CLICK THE LINK:')
    print('This only has to be done once.')

def get_access_token(code):
    state = request.args.get('state')
    url = '%soauth/v2/token' % BASE_OAUTH_API_URL
    data = {
        'code': code,
        'client_id': CLIENT_ID,
        'client_secret': CLIENT_SECRET,
        'redirect_uri': REDIRECT_URL,
        'scope': 'ZohoMail.messages.CREATE,ZohoMail.accounts.READ',
        'grant_type': 'authorization_code',
        'state': state
    headers = {'Content-Type': 'application/x-www-form-urlencoded'}
    r = requests.post(url, data=data, headers=headers)
    data = json.loads(r.text)
    ZOHO_DATA['access_token'] = data['access_token']

def get_account_id():
    url = BASE_API_URL + 'accounts'
    headers = {
        'Authorization': 'Zoho-oauthtoken ' + ZOHO_DATA['access_token']
    r = requests.get(url, headers=headers)
    data = json.loads(r.text)
    ZOHO_DATA['account_id'] = data['data'][0]['accountId']

def send_mail(body, email_address):
    url = BASE_API_URL + 'accounts/%s/messages'
    url = url % ZOHO_DATA['account_id']
    data = {
       "fromAddress": FROM_EMAIL_ADDR,
       "toAddress": email_address,
       "ccAddress": "",
       "bccAddress": "",
       "subject": "Test E-Mail",
       "content": body,
       "askReceipt": "no"
    headers = {
        'Authorization': 'Zoho-oauthtoken ' + ZOHO_DATA['access_token']
    r = requests.post(url, headers=headers, json=data)

def refresh_auth():
    # Update the access token every 50 minutes using the refresh token.
    # The access token is valid for exactly 1 hour.
    while True:
        url = (
        ) % (BASE_OAUTH_API_URL, ZOHO_DATA['refresh_token'], CLIENT_ID, CLIENT_SECRET)
        r = requests.post(url)
        data = json.loads(r.text)
        if 'access_token' in data:
            ZOHO_DATA['access_token'] = data['access_token']
            print('refreshed', ZOHO_DATA)
            time.sleep(3000)  # 50 minutes
            # Retry after 1 minute

@app.route('/callback/', methods=['GET', 'POST'])
def zoho_callback_route():
    code = request.args.get('code', None)
    if code is not None:
    return 'OK', 200

@app.route('/sendmail/', methods=['GET', 'POST'])
def send_mail_route():
    # Send a HTML email!
    data = ['1', '2', '3']
    mail = render_template('mail_template.j2', data=data)
    send_mail(mail, TO_EMAIL_ADDR)
    return 'OK', 200

def main():
    t = threading.Thread(target=refresh_auth)

if __name__ == '__main__':
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