Using Email API vs SMTP Relay: Which is Better in 2023

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This article is all about Email API vs SMTP relay. We will discuss the differences between Email API and SMTP relay and the pros and cons of using Email API and SMTP relay. We will focus more on which Email transfer method is better for sending emails and why you should use it.

email api vs smtp
SMTP vs Email API

When you want to send emails through an email service provider, you come up with the question of whether to use email API vs SMTP relay. You should make your decision based on your sending needs, priorities, and coding knowledge level. 

In this article, we will guide you through some pros and cons of both email transfer methods so that making a choice will be a no-brainer.

In this article, we will cover the following topics.

  1. Comparison Table, Email API vs SMTP
  2. What is an Email API?
  3. What is SMTP Relay?
  4. How does SMTP work?
  5. What are some Pros and Cons of using an Email API?
  6. What are some Pros and Cons of using SMTP to Send Emails?
  7. Which Email Transfer method is better for sending Emails?

Comparison Table of Email API and SMTP, Which one to Use for Sending Emails

How It worksSMTP – Simple Mail Transfer ProtocolThe client and the server communicate using multiple back-and-forthsHTTP – Hyper Text Transfer Protocol
Your app sends HTTP requests to use integrated functions of a third-party service
ProsEasy to set up
Simpler troubleshooting
Fast email delivery
No blockage
Optimized security
Analytics capabilities
ConsSlow performance for bulk email
Changing deliverability of emails
Possible blockage of port 25
Complex solution that requires coding skills
Unlike SMTP, HTTP API does not have a unique specification
Ease of testingYesNo
Mailtrap Email API applicabilityYesYes
Best Option forCasual email senders
integration with a CRM system or mail client
bulk email senders
app developers
Comparison Table of Email API and SMTP

If the above table has triggered interest, you are welcome to read more. 

What is an Email API?

An API (Application Programming Interface) helps to interact with two or more tools. With an email API, an application or website can interact with an email service provider to send an email message directly from the app or website.

For example, if you want to purchase on an e-commerce website, you instantly get a shipping notification in your mail besides the push notification from the app. This automated email sending is made possible through an email API.

An email API allows email service companies to access email services such as generating and sending transactional emails, managing email templates and lists, analyzing email marketing metrics, setting up domain authentication, and more.

Email APIs have two main categories: Transactional and contextual.

Transactional email APIs are designed for sending bulk or routine emails like notifications, password reset emails, and mass marketing campaigns through third-party platforms. MailChimp and SendGrid are the best examples of well-developed transactional email API providers.

Contextual email APIs are made to embed robust email connectivity directly into the software applications. Productivity tools, such as CRMs, applicant tracking systems, and even car consoles, use contextual email APIs to embed email functionality into the application. Contextual emails allow us to sync, send, receive, and collect analytics. The Nylas Email API is the best example of a contextual email API provider.

The list of the 10 best email API tools you can use.

What is SMTP Relay?

When servers are located on different domains, an SMTP relay is used to send emails between SMTP servers.

SMTP stands for (Simple Mail Transfer Protocol). It is an email protocol used for sending email messages from one email account to another via the internet.

The Email protocols are sets of rules that allow different email clients and accounts easily exchange information. It is the only dedicated protocol for sending emails. Most email clients, such as Outlook, Apple Mail, Gmail, and Yahoo Mail, rely on SMTP to “push” or send messages from a sender to a recipient.

An email SMTP relay service is used every time you send an email to someone outside your address’s domain. SMTP, or Simple Mail Transfer Protocol, does the heavy lifting of sending the message. The relay service sends the message from your email server to the recipient’s email server.

How Does SMTP Work?

To explain how SMTP works, we need to go over the sending process, the individual rules and commands that power it, and the errors you may encounter. 

First, we need to create an SMTP server. Once we establish an SMTP server, the email clients can connect and communicate with it. When the user clicks on “send” on an email message, the email client opens the SMTP connection to the server so it can send. 

From there, the SMTP client uses the commands to tell the server what to do and transfer data, like the sender’s email address, the recipient’s email address, and the email’s content. The Mail Transfer Agent or Message Transfer Agent (MTA) checks to see if both email addresses are from the same email domain, such as

  • If they are the same, it sends the email right away.
  • If not, the server uses the Domain Name System (DNS) to identify the recipient’s domain and send it to the correct server.

What are some Pros and Cons of using an Email API?

As we already learned, what an Email API is. Now, let’s look at some pros and cons of using an email API.


Here are the advantages of using an email API for sending Emails.

  1. Quick Email Tranfer.

One of the advantages of using an email is fast email transfer. There is less back-and-forth communication between servers using an API, which results in more immediate delivery.

  1. Analytics.

Analytics is essential for any meaningful assessment of your email campaigns. Unlike SMTP, an email API usually provides statistical insights into recipient-email interactions like email deliverability, open rate, unsubscribes, and more.

The email API providers allow you to track important metrics such as the number of successful messages delivered, how many messages were rejected by an ISP, why the messages were not being delivered, how many recipients opened the message, or how many call-to-action links were clicked.

  1. Security.

You need to use an API key when you use an email API to send emails. This way, it protects your website or application from phishers or spammers. 


 Here are the disadvantages of using an Email API.

  1. Requires Coding Knowledge.

Setting up and running an email API is difficult, as it relies heavily on your expertise in using a programming language and the client libraries. Even if you have detailed documentation, understanding and implementing it for email sending can be a real challenge.

  1. Needs Repeated Updates.

Unlike SMTP, as we know, the API versions change with each passing year. So you will have to keep an eye open for updates and make changes to suit the new protocols.

What are some Pros and Cons of using SMTP to Send emails?

As we have already understood what SMTP is. Now, let’s discuss some pros and cons of using SMTP for sending emails.


  1. No Hassle With Setup.

One of the advantages of using SMTP is an easy setup. All you need to do is enter your SMTP credentials to your mail user agent. And after that, you can send emails right from your system. No coding skills are required to do that.

  1. Platform Independent.

STMP is platform-independent. It means that the SMTP connection has no specific restrictions that the app or system must integrate.

  1. Detailed Conversation Between the Client and Server.

One of the advantages of using SMTP is that it provides detailed conversations between the client and server. Each command that the client sends to the server gets a response code, which always includes context. You will get an idea of what went wrong if there is an error.


  1. Bad Choice for Bulk Emails.

SMTP would be a bad choice for sending bulk emails because it requires multiple communications between the client and the server. This increases the error rate and slows down the sending of bulk emails. Furthermore, you will have to deal with Mail Merge and MIME.

  1. Changing Deliverability.

As we know, most SMTP relay services use shared IP addresses, which can affect the sender’s reputation. That’s why its rate may change all the time. A white-label email marketing software can be a solution, but it requires some DNS tweaks. 

  1. Blocked SMTP Ports.

When using SMTP, some environments may block SMTP due to built-in or firewall restrictions. Mostly, this refers to port 25, one of the most abused ports for spamming. All these issues can be solved, but it will take much time and effort.

Which Email Transfer method is better for sending Emails?

Neither email API nor SMTP is the only protocol for sending emails. The choice between using an email api vs smtp relay depends on your sending needs. 

An email API is perfect for app developers because they have the necessary programming knowledge. Because of its high and fast delivery, Email API is also beneficial when sending bulk emails. Sending through email API is more secure because API keys provide detailed statistics. Yet, you must stay up-to-date with all the changes email API frequently undergoes. 

The SMTP seems more suitable if you are an occasional sender and are not focused on sending emails in high volume. Even though the email deliverability may not always be stable because of multiple back-and-forths between servers, it is universal and easy to set up. 

And once you configure the SMTP relay, you do not need coding knowledge to send an email using this protocol. 

Good luck with making a choice!

This article explains what an Email API is and what SMTP is. It also explains the pros and cons of email API and SMTP methods and how does STMP work.

The article also explores which email transfer method is better for sending emails.

I hope you’ve enjoyed the article. Stay tuned for more at FuelingPHP

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