The Ultimate Guide to Choosing Email Marketing API for Your Business: HTTP or SMTP

Email marketing remains one of the most effective digital marketing channels. However, delivering emails at scale requires proper email infrastructure.

When using an external email service provider (ESP), the two main options for sending email programmatically are:

• SMTP API
• HTTP API

SMTP stands for Simple Mail Transfer Protocol. It’s the standard protocol for sending email directly from one server to another. An SMTP API is basically an implementation of SMTP, with some extra features.

HTTP API allows email to be sent through HTTP requests, instead of SMTP. Each ESP implements an HTTP API in its own way, with a unique set of methods.

Instead of managing your own SMTP servers, you outsource the delivery to dedicated email services. The main benefits are simplicity, speed, and versatility. You don’t have to maintain email servers or worry about infrastructure limitations.

While most ESPs offer both SMTP and HTTP APIs, each of the two has its own advantages and drawbacks. So, how do you choose the right one for your business?

In this comprehensive guide, we’ll compare SMTP vs HTTP API for email marketing across several criteria.

Overview of SMTP and HTTP APIs

What is SMTP?

SMTP, or Simple Mail Transfer Protocol, is the standard way of sending emails across the internet. An SMTP API service allows developers to easily integrate email-sending capabilities into their applications, providing more flexibility and control over the email delivery process.

SMTP is used for server-to-server transfer of emails as well as for the initial submission of emails to an SMTP server. When you send an email from a client app like Thunderbird or Outlook, under the hood, they use SMTP to transfer your email to the designated email server. A similar client-side mechanism is often implemented in CRM systems, blog platforms and other software.

What are HTTP APIs for Email?

Sending email via HTTP APIs involves your application making an API call to an email service like Mailgun or SendGrid with your email content and recipients. The email service then sends the email to recipients using its own SMTP infrastructure.

Ease of Use

SMTP API

When it comes to simplicity, nothing beats the SMTP API. Connecting your SMTP-capable app to an external SMTP service usually takes minutes, quite literally. All you need is change a few settings like server address, port number, and login credentials to the values given by your provider. To use features beyond the usual SMTP capabilities, however, you need to add custom headers to your emails, which will require a bit of programming, but not much.

HTTP API

In contrast, email HTTP APIs may require quite some time to master and integrate with your existing software. As mentioned above, each ESP takes a slightly different approach to implementing this type of API, so you’ll need a closer look at particulars. High level libraries for most popular programming languages are usually provided, but the integration process still requires programming and may take significant time.

Speed

HTTP API

Speed is the area where HTTP APIs really shine. This method has far less protocol overhead, compared to regular SMTP. Besides, you don’t need to make multiple requests to send similar messages to several customers – both email body and substitutions will be sent in a single API request. Depending on the provider’s infrastructure, an HTTP API may allow you to submit millions of emails hourly. If speed is your top priority, HTTP API is the way to go.

SMTP API

To send a single message using SMTP, the two parties are exchanging multiple requests and responses. This makes SMTP APIs way slower, the typical sending volumes for this option do not exceed tens of thousands of emails per hour.

Versatility

SMTP API

SMTP APIs usually offer little to no extra features, beyond those outlined in the SMTP specification. Additional functionality is accessed via non-standard headers in your submitted emails. To add these, you’ll need to do some extra coding, which does not align with the idea of maximum simplicity. 

HTTP API

HTTP APIs are generally very versatile, offering a large number of API methods, besides email submission. Additional features may include email validation, project and template management, setting webhooks, managing suppression lists, and more.

When should you use SMTP APIs?

If your email needs are simple, low-volume, and less time-critical — such as transactional emails for a small web app — running your own SMTP servers may suffice. This approach allows you to avoid external costs but requires you to manage infrastructure and handle necessary security controls. Migrating from this in-house solution to an ESP using SMTP API is extremely smooth and easy.

When should you use HTTP APIs?

For business-critical communications at any reasonable scale, a hosted HTTP API service is the superior choice. The benefits of enhanced speed, scalability, flexibility, and cost-effectiveness make HTTP APIs indispensable for professional-grade email capabilities. 

We hope this guide helps you understand the SMTP vs. HTTP API choice and choose the right email delivery method for your business needs.

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