This has been an ongoing issue with my site for some time now. I had a solution to it before and had no issues but recently it has popped back up again with my post call to my function endpoint.
This my lambda function which accepts a json request object which uses it to interact with an smtp request
const nodemailer = require('nodemailer');
require('dotenv').config()
exports.handler = async (event, context) => {
// const headers = {
// 'Content-Type': 'application/json',
// /* Required for CORS support to work */
// 'Access-Control-Allow-Origin': '*',
// 'Access-Control-Allow-Methods': 'POST',
// 'Access-Control-Allow-Headers': 'Content-Type',
// /* Required for cookies, authorization headers with HTTPS */
// 'Access-Control-Allow-Credentials': trued
// };
const request = JSON.parse(event.body);
const validation = {
name: request.name.length > 0,
email: /^[a-zA-Z0-9.!#$%&’*+/=?^_`{|}~-]+@[a-zA-Z0-9-]+(?:\.[a-zA-Z0-9-]+)*$/.test(request.email),
message: request.message.length > 6 && request.message.length < 1001
}
const isValid = Object.keys(validation).every(field => field);
if(!isValid) {
return {
statusCode: 400,
// headers,
body: JSON.stringify({
response: "Your request failed validation. Please try again in the next few moments",
})
}
}
let transporter = nodemailer.createTransport({
host: process.env.SMTP_DOMAIN,
port: process.env.SMTP_PORT,
secure: true,
auth: {
user: process.env.SMTP_USERNAME,
pass: process.env.SMTP_PASSWORD
}
})
transporter.verify(function(error, success) {
if (error) {
return {
statusCode: 503,
// headers,
body: JSON.stringify({
response: "Uh oh! It looks like the messaging service is not available. Please try again later or reach out to me personally."
})
}
} else {
console.log("Server is ready to take our messages");
}
});
let info = await transporter.sendMail({
from: `"Portfolio Contact Form" <${request.email}>`,
to: process.env.EMAIL_TO,
subject: request.name,
text: request.message
})
return info.response == "250 Great success" ? {
statusCode: 200,
// headers,
body: JSON.stringify({
response: "Your message has been successfully received!",
})
} : {
statusCode: 500,
// headers,
body: JSON.stringify({
response: "Hmmm... something went wrong while sending your message. Try back at a later time or email me personally"
})
}
}
And my client request
const api_address = '@@api_address/.netlify/functions'
const postContactMessage = async (data) => {
return await fetch(`${api_address}/contact`, {
method: 'POST',
body: JSON.stringify(data),
headers: {
'Content-Type': 'text/plain',
// 'Content-Type': 'application/x-www-form-urlencoded',
}
});
}
As you can see, I originally hardcoded a header to attach to the response to try to resolve the cors issue in the past. However, when a user attempts to send a contact message to the endpoint, the server picks up the request, sends a response, and the browser rejects the response object.
I understand what the issue is but I don’t quite undestand how to resolve the issue. I’ve tried uncommented the header and adding it with the response, and making a series of adjustments on my request object but no avail.
The solution maybe quick and easy but I’m at a point of befuddlement that it doesn’t look apparent to me.
Thanks to everyone who is reading this and taking time out of their day to help me with this 
Dan