How to Use Flutter to Send an OTP Code by Email

Configuring the OTP Email Frontend with Flutter

Using Flutter Frontend with Dart

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: Text('Send OTP')),
        body: OTPForm(),
      ),
    );
  }
}
class OTPForm extends StatefulWidget {
  @override
  _OTPFormState createState() => _OTPFormState();
}
class _OTPFormState extends State<OTPForm> {
  final TextEditingController _emailController = TextEditingController();
  final TextEditingController _otpController = TextEditingController();
  Future<void> _sendOTP() async {
    final response = await http.post(
      Uri.parse('https://your-backend-url/send-otp'),
      body: {'email': _emailController.text},
    );
    if (response.statusCode == 200) {
      ScaffoldMessenger.of(context).showSnackBar(SnackBar(content: Text('OTP sent!')));
    } else {
      ScaffoldMessenger.of(context).showSnackBar(SnackBar(content: Text('Failed to send OTP')));
    }
  }
  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.all(16.0),
      child: Column(
        children: [
          TextField(
            controller: _emailController,
            decoration: InputDecoration(labelText: 'Email'),
          ),
          SizedBox(height: 20),
          ElevatedButton(
            onPressed: _sendOTP,
            child: Text('Send OTP'),
          ),
        ],
      ),
    );
  }
}

Building the OTP Email Sending Backend

Express and Node.js for backend development

const express = require('express');
const nodemailer = require('nodemailer');
const bodyParser = require('body-parser');
const app = express();
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));
app.post('/send-otp', async (req, res) => {
  const { email } = req.body;
  const otp = Math.floor(100000 + Math.random() * 900000);
  let transporter = nodemailer.createTransport({
    service: 'gmail',
    auth: {
      user: 'your-email@gmail.com',
      pass: 'your-email-password',
    },
  });
  let mailOptions = {
    from: 'your-email@gmail.com',
    to: email,
    subject: 'Your OTP Code',
    text: `Your OTP code is ${otp}`
  };
  try {
    await transporter.sendMail(mailOptions);
    res.status(200).send('OTP sent');
  } catch (error) {
    res.status(500).send('Failed to send OTP');
  }
});
const PORT = process.env.PORT || 3000;
app.listen(PORT, () => {
  console.log(`Server running on port ${PORT}`);
});

Commonly Asked Questions Concerning OTP Email Sending

1. How can I use SendGrid to send an OTP email?
2. To send emails from your Flutter app, you must create a SendGrid account, get an API key, and utilize the SendGrid Dart package.
3. What advantages come with utilizing email APIs from third parties?
4. SendGrid and other third-party email APIs provide high delivery rates, spam protection, and extra capabilities like analytics and tracking.
5. Can I use SendGrid without using Mailgun?
6. Yes, Mailgun is yet another top-notch email sending choice. By leveraging its API and setting it up in your Flutter project, you may integrate it in a similar way.
7. And if my emails end up in the spam folder?
8. You can lower the likelihood that your emails will be tagged as spam by using trustworthy third-party email providers like SendGrid or Mailgun.
9. What should I do when my OTP expires?
10. The OTP and its timestamp can be kept in your backend, and you can validate it in a set amount of time—usually five to ten minutes.
11. Is sending OTPs by email secure?
12. Emailing OTPs is a convenient way to send them, even though it's not as secure as SMS. To protect user data, make sure you use HTTPS and other security measures.
13. Is it possible to alter the OTP email template?
14. Yes, you can alter the email's content and format to better align with the branding of your application using the majority of email APIs.
15. If the OTP email does not go through, what should I do?
16. Incorporate error handling into your backend so that you may advise the user to try again or retry sending the email.
17. How can I confirm the OTP that the user entered?
18. Verify the OTP that the user entered and the one that is kept in your backend. The OTP is confirmed if they coincide and fall within the allowed window of time.

Concluding the OTP Email Procedure

In a Flutter application without Firebase, setting up OTP email verification requires properly configuring the frontend and backend. It is possible to streamline the procedure and improve email delivery dependability by utilizing third-party providers like SendGrid or Mailgun. You are guided through the installation process by the offered scripts and processes, which guarantee a smooth user verification experience. To keep your application's integrity, make sure you handle OTP expiration and security.