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Which Protocol Should I Use To Send Email, SMTP Or REST?

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06 Jan 2021

People tend to have more than a single account for multiple purposes. For instance, one might have two different email accounts for office and personal use, separating work from home.

The expected average user ratio is rising by the day and is expected to reach a high of 1.86 by the next two years. Since people have more than one account, there are several protocols to facilitate everyone and ensure the timely delivery of all of your emails.

A protocol is an intermediary between a sending server and anreceiving server, just like sending mail via post. However, when it comes to email marketing campaigns, you have to send hundreds of email messages in bulk at a particular time. This leads to a question, Which protocol should I use to send bulk emails?

Here's a detailed insight into using SMTP or REST APIs.

Email Protocols: SMTP or REST API?

For sending out transactional and bulk emails, there are two options mainly, SMTP and API. SMTP is short for Simple Mail Transfer Protocol, whereas API is short for Application Programming Interface.

Sending Emails via SMTP

Simple Mail Transfer Protocol (SMTP) is the standard protocol that is used for email communication since 1982. SMTP is basically a set of rules, methodology, and the components of an email message. Moreover, it is essentially how you send an email in a standard format that can be received by an email server.

Advantages of SMTP

SMTP is the most widely used of the two protocols. In terms of integration and ease of use, SMTP has proven to be more beneficial than API. Nowadays, every phone and computer is able to use SMTP. Moreover, setting up SMTP is relatively easy, and all you need to do is create an account. An email account powers your email apps run by your Email Service Provider (ESP).

In case you run into any errors with SMTP, you will receive a 400 or 500 error code message that provides you with vital information into what went wrong. Here are the pros of sending emails via SMTP at a glance

Now that we've discussed the benefits and ease of use of the SMTP, lets head over to some of the issues related to using SMTP.

Disadvantages of SMTP

While using SMTP as a mailing protocol might be easy, but it has certain drawbacks. It requires multiple communication attempts with the server. Furthermore, it requires DNS, Email authentication, and other verification factors. Besides, merging your mail with SMPT can be a challenging and time-consuming process.Cons of Sending Emails via SMTP at a glance,

Results in slow performance of sending bulk emails

Changing deliverability of emails

Possible blockage of port 25

Sending Emails via REST API

API is short for an application programming interface. It enables you to integrate multiple apps for your mailing needs. An API is also referred to as Web API, or HTTP API -aninterface where communication relies on HTTP (HyperText Transfer Protocol).

REST is short for "Representational State Transfer." It is a set of rules used by developers to create an API and determines its appearance. These rules involve the process of requesting the user for a specific piece of data, referred to as "Resource" when you link it to a web URL.

Each of these web URL is known as a request, whereas the data received is known as a response. Here are some benefits of using REST APIs for sending emails.

Advantages of REST API

API enables you to send out bulk emails with ease. In addition, it allows you to automate the email sending process using your app. It features better delivery speeds and can be executed within seconds. Moreover, with fewer communication attempts with the server APIs ensure faster delivery.

For marketers to get the most out of their digital marketing campaigns, APIs can provide email statistics with seconds. APIs can be enabled for use with targeted action-based emails to ensure the right message is delivered to the right person.Pros of sending Emails via APIs at a glance

Using APIs has certain drawbacks as well. APIs are relatively difficult to set up and requires a certain level of knowledge in programming. Due to the coding involved, it might get challenging to resolve issues. Furthermore, APIs require constant updates with the day to day updates in trends.

Cons of sending Emails via APIs at a glance

Protocol for Sending Email: SMTP vs REST

When choosing between SMTP and REST API, it all comes down to the complexity of your project or business organization. Both the protocols focus on providing a stable and high rate of email deliverability. However, when it comes to the methodology and operation, they differ. SMPT involves a series of back and forth communication between the sending server and the receiving server. SMTP is simple and easy to use.

In contrast, REST API has no back and forth communication between the client and the receiving end, which results in faster delivery of your emails. Furthermore, the REST API is not limited to sending out emails only. It can also provide you with analytics on your email marketing campaigns and provide you with real-time information on how well your campaign is running. REST APIs are often preferred for sending out bulk emails, especially when using CBT Mass Email Sender, but the only downside to using this is it requires a certain level of coding experience. At the end of the day, it all comes down to the ease of use of these protocols and your preferences.


Both SMTP and REST APIs are email protocols that ensure the ideal delivery of your emails. SMTPs are easy to set up and require no effort, whereas APIs require a certain level of programming expertise to set it up correctly.

APIs can provide you with a lot more than just sending out emails. It enables you to view real-time analytics and send out emails quicker due to the lack of to and fro communication between the sending and the receiving server.

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