Decoding Email Tech: SMTP vs. API

Oct 18, 2023 | Blog, Deliverability

In modern communication, email remains a fundamental tool for personal and professional interactions. Behind the scenes, SMTP (Simple Mail Transfer Protocol) and APIs (Application Programming Interfaces) play critical roles in ensuring the smooth transmission and reception of emails. In essence, SMTP and API can be seen as two different approaches to setting up your email platform for sending and receiving information (however, the API term does not exclusively apply to the world of emails).

Understanding the difference between SMTP and APIs can be quite beneficial, especially for those involved in email communication, as it gives insight to what’s happening behind the scenes in your email setup. By understanding this, you can further answer the question: Is my company using the right approach in our setup?

In this blog post, we’ll dive into these two essential components and shed light on their respective functionalities and purposes.

So, what’s the difference between SMTP and API?

SMTP and APIs are indispensable components of email communication, each serving a unique purpose in the digital landscape. SMTP acts as the primary protocol for sending and routing emails, ensuring the reliable delivery of messages. On the other hand, APIs offer a more flexible and feature-rich interface, enabling applications to interact with email services, send personalized emails, and manage email-related tasks efficiently.

While SMTP will demand a request per email you send, the API solution is more fit for bulk mails. It will simply take too long to send a large number of emails using SMTP.

Often, SMTP is used for transactional emails, such as user information, order confirmation, password reset etc., while the API solution is more suitable for marketing emails. In relation to this, the SMTP solution can be seen as an email cannon for raw emails, while the API solution is more relevant if you want to design your emails (for marketing purposes).  

Most webshops give you the possibility of setting op an SMTP solution after you have provided some basic information. This means that you have a mail cannon for transactional emails very quickly – but you do not have the possibility of styling and setting up automated emails, as this would require the API solution.

For a further technical understanding, read more bellow.

SMTP: The Engine of Email Transmission

SMTP, or Simple Mail Transfer Protocol, is the protocol responsible for sending, receiving, and relaying email messages between servers. Essentially, it’s the engine that powers the transmission of emails across the vast network of servers that comprise the internet.

Key Characteristics of SMTP:

  1. Send-Only Protocol: SMTP is designed to send emails from the sender’s email client or application to the recipient’s mail server.
  2. Port 25: SMTP traditionally operates on port 25, allowing for communication between the sender’s mail server and the recipient’s mail server.
  3. Text-Based Protocol: SMTP utilizes a text-based protocol, making it relatively simple to use and understand.
  4. Message Format: SMTP defines the format of an email message, including the headers, body, and attachments, ensuring standardized communication.
  5. Reliable Message Delivery: SMTP ensures reliable message delivery through error reporting, message queuing, and retransmission mechanisms.

While SMTP is vital for initiating and managing email communication, developers often turn to APIs to interact with email services and integrate email functionality into applications.

APIs: Bridging the Gap between Applications and Email Services

APIs, or Application Programming Interfaces, serve as a bridge between different software systems, allowing them to communicate and share data seamlessly. In the context of email, APIs enable applications to interact with email services to send, receive, and manage emails programmatically.

Key Characteristics of APIs for Email:

  1. Bidirectional Communication: Unlike SMTP, which is unidirectional, APIs allow for bidirectional communication, enabling applications to both send and receive email data.
  2. Structured Data Exchange: APIs facilitate structured data exchange, often using standardized formats like JSON or XML, allowing for more complex and customized interactions.
  3. Authentication and Security: APIs typically require authentication, ensuring that only authorized users or applications can access and use the email services.
  4. Flexible Functionality: APIs offer a wide range of functionalities beyond just sending emails, such as managing contacts, accessing email history, and setting preferences.
  5. Integration Capabilities: APIs can be easily integrated into various applications, websites, or software platforms to automate email-related tasks and enhance user experience.

In essence, APIs provide a more versatile and sophisticated way to interact with email services programmatically compared to the fundamental capabilities of SMTP.


Understanding the difference between SMTP and APIs empowers email marketeers and businesses to make informed decisions regarding the integration and utilization of email communication in their applications, ultimately enhancing the overall user experience and workflow efficiency. Whether you’re building a simple email client or a complex email marketing platform, leveraging both SMTP and APIs effectively can significantly enhance your email functionality.

Heysender blog

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