A netlify ready serverless function for sending email with MailJet API

send-email-mailjet.js

const Mailjet = require ('node-mailjet')
const mailjet = new Mailjet({ 
    apiKey: process.env.MJ_APIKEY_PUBLIC || 'your-public-api-key',
    apiSecret: process.env.MJ_APIKEY_PRIVATE || 'your-private-api-key'
  });

exports.handler = async (event) => { 

  const { fromEmail, fromName, toEmail, toName, subject, TextPart, HtmlPart } = JSON.parse(event.body);

    const request = mailjet
        .post('send', { version: 'v3.1' })
        .request({
          Messages: [
            {
              From: {
                Email: fromEmail,
                Name: fromName
              },
              To: [
                {
                  Email: toEmail,
                  Name: toName
                }
              ],
              Subject: subject,
              TextPart: TextPart,
              HTMLPart: HtmlPart
            }
          ]
        });

        request
            .then((result) => {
                console.log('email inviata: ', JSON.stringify(result.body))
            })
            .catch((err) => {
                console.log('errore invio email: ', JSON.stringify(result.body))
        });

        return {
            statusCode: 200,
            body: JSON.stringify({ message: "email sended correctly." }),
        }
        
}

// frontend code for sending a email with the upper netlify function (this code is not tested)

      // const data = {
      //   fromEmail: 'info@example.com',
      //   fromName: 'Name Surname',
      //   toEmail: '@example_2.com',
      //   toName: 'Name Surname',
      //   subject: 'This is the title',
      //   TextPart: 'This is the main email text',
      //   HtmlPart: 'This is the main email text.'
      // };

      // const r = await fetch('./netlify/funcions/send-email', {
      //   method: 'POST',
      //   headers: {
      //     'Content-Type': 'applicazion/json'
      //   },
      //   body: JSON.stringify(data),
      // }).then((res)=> res.json());

Put this on "/functions/send-email-mailjet.js".

To make it work you need to install the node-mailjet package within the /function directory like this from command line:
cd functions && npm install node-mailjet

Now you can use in the frontend like this:

      const data = {
        fromEmail: 'info@castenettoa.com',
        fromName: 'castenettoa.com',
        toEmail: 'castenetto.andrea@gmail.com',
        toName: 'Andrea Castenetto',
        subject: 'Un nuovo servizio è stato acquistato.',
        TextPart: 'Complimenti. Vai su stripe per saperne di più.',
        HtmlPart: 'Complimenti. Vai su stripe per saperne di più.'
      };


      const r = await fetch('./netlify/funcions/send-email', {
        method: 'POST',
        headers: {
          'Content-Type': 'applicazion/json'
        },
        body: JSON.stringify(data),
      }).then((res)=> res.json());