A naive mailing lib with multiple email service providers integrated.

Usage no npm install needed!

<script type="module">
  import vicdotdevMailerHub from '';



This package integrates multiple email service providers e.g. MailGun, SendGrid, when you use this package to send an email, it will try to send an email with each of its integrated services until success. That means, as long as you have at least one email service provider up and running, the email will be sent successfully.

As this package is still at its unstable version, you are not encourage to use at the moment.

Currently MailGun and SendGrid are supported, more email services might be added in later.

Getting Started

  • install the package
  npm install --save @victordotdevelop/mailer-hub
  • set up mailer hub with your own api keys (you can sign up at MailGun and SendGrid's site)
  • then try to send an email
    const mailerHubLib = require('vicdotdev-mailer-hub');
    const makeMailerHubBuilder = mailerHubLib.makeMailerHubBuilder;
    const ErrorTypes = mailerHubLib.ErrorTypes;

    // set up mailers, i.e. email service provider
    const builder = makeMailerHubBuilder();
    const mailHub = builder
        apiKey: 'key-xxxxxxxxxxxxxxxxxxxxxxxxxxx',
        domain: '',
        senderAcc: 'postmaster',
        domain: 'sendgrid.sandbox',
        senderAcc: 'postmaster',

    // send an email
        to: '',
        cc: '',
        bcc: '',
        subject: 'Sample code: how to send email with this package',
        text: `And more information in paragrahs`,
    .then(() => {
      console.log('email was sent sucessfully');
    .catch((err) => {
      if (err instanceof ErrorTypes.IncompleteMailError) {
        // this means you did not provide enough fields: to, subject, text
      if (err instanceof ErrorTypes.AllMailerFailError) {
        // this means all of your email services provider failed to send this email

Note that you can also pass an array of email addresses for to, cc, bcc

TypeScript support

This project was written in typescript. You can look for function signatures from the .d.ts.


If you want to further develop this package by your own:

  git clone <this repo github clone address>
  cd <this repo>
  npm intall

Run the tests

Note that you have to to rename ./src/tests/data/secret/xxxxx.secret.exmaple.ts back to ./src/tests/data/secret/xxxxx.secret.ts. Then fill in your own api keys and domain settings in the files. Then you can run

  npm test

Caution: If you are using MailGun's sandbox domain, running these tests will use up your sandbox message limit pretty quickly, by that time your tests against MailGun service will fail, and you will see console error messages Error: message limit reached


  npm run build

Directory Structure

Below shows a glance of the source code folder

  ├── errors.ts                               # publicly exposed error types
  ├── index.ts                                # lib entrance
  ├── interfaces.ts                           # interfaces (data model)
  ├── mailer-hub.ts                           # main component, the abstraction layer of multiple email services
  ├── mailers                                 # specific email service providers
  │   ├── mailgun.ts
  │   └── sendgrid.ts
  └── tests                                   # test files and data
      ├── data
      │   ├── emails.ts
      │   └── secret
      │       ├── mailgun.secret.exmaple.ts
      │       ├── mailgun.secret.ts           # this is not committed to git repo. you have to fill in your own.
      │       ├── sendgrid.secret.example.ts
      │       └── sendgrid.secret.ts          # this is not committed to git repo. you have to fill in your own.
      ├── index.spec.ts
      ├── mailer-hub.spec.ts
      ├── mailers
      │   ├── mailgun.spec.ts
      │   └── sendgrid.spec.ts
      └── send-mail.spec.ts

Major Components

Below shows the major components in this package.

major components

  • IMailerHub: This is the object to be used by other parties to send an email
  • MailerHubBuilder: Users are supposed to input their configuration of different email service provider(i.e. _mailer) and build a IMailerHub object
  • IMailer: one IMailer represents exatly one specific email service provider.
  • sendOnce: a core function responsible for sending ONE successful email among many email servicer providers(they are called mailers in code). This function plays the logic of fail over.


  • Validate credentials of different email service providers upon the creation of
  • Log each time of send email and how many services were tried. Expose the log for pakcage users to retrive. E.g. via events;