How To Send Emails Using an Email API

What is an Email API? An email API (Application Programming Interface) lets developers send and…


What is an Email API?

An email API (Application Programming Interface) lets developers send and receive emails on behalf of their users without building email functionality from scratch. Email APIs achieve this by connecting directly with email service providers (ESPs) such as Microsoft Outlook, Gmail, or iCalendar. Instead of building custom integrations with an ESP, you can use an email API to make calls that access data or execute operations, such as sending an email. 

By sending messages through an email API, not only can you conserve developer time and resources, but you can also make your end-users more productive and improve the performance of their email sends. However, not all email APIs are created equal: some offer support for massive marketing campaigns or transactional product updates, while others support contextual, conversational email use cases

In this post, we’ll review the benefits of using an email API to send emails, what to look for when selecting a solution, and our best practices for programmatically sending email that lands in the inbox, not SPAM.  

Benefits of sending emails with an API

Building email API integrations within your application gives you complete control over the sending experience, allowing you to quickly deliver features that maximize engagement and conserve resources. Implementing the right email API can provide the following benefits:

Benefits for engineering and product teams:

  • Conserve developer resources – Building a custom integration to send email requires reverse-engineering decades of email protocols. You’ll need the resources and expertise to deliver a full-featured sending experience for your users. Luckily, Email APIs abstract away most of the work of building send functionality, providing a single, normalized point of integration that can shave months off your development time and conserve up to 50% of your developer resources.  
  • Maximize in-app engagement – Your users don’t want to waste time context-switching between their email client and your application. By embedding email send functionality, you can provide additional value to your users, keeping them engaged in your application for longer periods. 

Benefits for users:

  • Sending at scale – Sending email with an API can make it easier to send high volumes of email, faster. Many email APIs also offer message tracking and analytics, which give users signals to improve the open, reply, and click-through rates of their email sends.  
  • Maximize deliverability – The right email API can help you deliver high volumes of email without suffering from poor deliverability. By ensuring high deliverability rates, you can build users’ confidence in your solution, improving customer loyalty. 
  • Automate manual email tasks – Sending emails can entail all kinds of manual, repetitive tasks. Sending personalized sales outreach emails, for example, can eat up time that can be better spent identifying and engaging new prospects. Email APIs make it easy to build experiences that save users meaningful time. 

What to consider when evaluating solutions to send emails programmatically 

When evaluating Email APIs on their sending capabilities, it’s important to have a clear understanding of your use case. Marketers, for example, need to send massive volumes of emails, well beyond provider rate limits. Sales reps need to send personalized, automated cadences to targeted lead lists. And customer support teams need emailing solutions that help them triage customer tickets and resolve issues faster. If you can identify your use case, you’ll have an easier time choosing the best solution for your needs. 

Let’s run through a few of the criteria you should consider before selecting an Email API:    

Transactional versus contextual email APIs

Transactional and contextual email APIs serve unique purposes in the world of email communication. Transactional email APIs are designed to send automated, one-time messages to recipients, based on in-product events (such as account activations, password resents, or order confirmations) or marketing campaigns (such as newsletters or promotions). Contextual email APIs are better suited to use cases that require send and receive capabilities, high email deliverability, and the ability to send directly from a user’s inbox. 

Want to learn more about the differences between transactional and contextual email APIs? Check out this blog post.

Universal connectivity 

If you’ve decided that a contextual email API is the right fit for your sending needs, one critical attribute is compatibility with email service providers. APIs that connect with a single protocol or service provider greatly limit your ability to expand support to new providers in the future. Choose an email API that standardizes data across all providers, allowing you to say “yes” to future customer requests and quickly stand up future integrations. 

High Email deliverability 

The email deliverability rate is the percentage of emails that successfully reach their intended recipient’s inboxes. While a number of factors impact deliverability, poor sender reputation is notorious among transactional email providers for tanking deliverability rates and eroding users’ trust in their sending solution. Choose an email API with high deliverability to improve user engagement, brand perception, and ROI. 

Message analytics 

The best email APIs offer out-of-the-box capabilities to track message open, reply, and click-through-rates. You can use the capabilities to surface critical performance metrics to your users, enabling them to maximize the impact of their email outreach. 

Managing Email replies and notifications

A critical aspect of sending email is managing replies. Most transactional providers offer resource-intensive workarounds for tracking and surfacing replies. If managing replies is a requirement for your email sending use case, consider an API that automatically notifies you of new replies and assigns them to the correct email thread. 

How to Use Email API to Send Emails

Using an email API to send emails is a simple task that we can perform just by calling our terminal window. Let’s take a look at an example:

curl --request POST \
  --url \
  --header 'Accept: application/json' \
  --header 'Authorization: Bearer <ACCESS_TOKEN>' \
  --header 'Content-Type: application/json' \
  --data '{
  "subject": "From Nylas",
  "to": [
      "email": "",
      "name": "Nylas"
  "body": "This email was sent using the Nylas email API. Visit for details."

While this is simple and straightforward, and allows us to call the API from any programming language that supports the REST architecture, it’s always better to have an SDK as it makes our development efforts lighter and easier.

Nylas provides SDKs for Python, Ruby, Java and Node.js, so we can create desktop, terminal or web applications.

Let’s take a look at a Ruby example:

#!/usr/bin/env ruby
# Import your dependencies
require 'dotenv/load'
require 'nylas'

# Initialize your Nylas API client
nylas =
    app_id: ENV["CLIENT_ID"],
    app_secret: ENV["CLIENT_SECRET"],
    access_token: ENV["ACCESS_TOKEN"]

# Send your email
    message = nylas.send!(to: [{ email: ENV["RECIPIENT_ADDRESS"], name: "" }],
    subject: "With Love, from Nylas", 
    body: "This email was sent using Ruby and the Nylas API.")
    puts "Message \"#{message.subject}\" was sent with ID #{}"	
rescue => error
# Something went wrong
	puts error.message

By using an SDK we can protect our credentials, and take advantage of using a robust programming language.

Get Started with Sending Emails with an Email API: Step-by-step

Step 1. Setup an account

  • Go to our registration page and sign up to get up to 10 connected accounts for free. No credit card is required.

Step 2. Get an API Key

  • Go to your Nylas Dashboard, and you will find your Client_id, Client_secret and Access_Token 

Step 3. Choose your favorite SDK

  • Choose from Python, Ruby, Java and Node.js

Step 4. Send an email

The Nylas Email API: The fastest and easiest way to send email

If you need an email API with universal connectivity to any email service provider, near-perfect deliverability, robust message analytics, and logic for seamlessly managing replies, the Nylas Email API is the best choice for your sending needs. With the Nylas Email API, you can stand up an email integration up to 12x faster than building from scratch. By connecting directly to users’ inboxes, you can build engaging, contextual email experiences in your application that make your users more productive.

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