Email API vs SMTP: Top Methods to Organize Email Sending

Manas Singh 12th Jul 2022

When you want to create an app with the email sending function you have to think about your method of email sending organization. There are two popular options that you can use for this purpose. The first one is called the Simple Mail Transfer Protocol and it is the most common choice in lots of cases.

However, there is still a popular Web API thing that may be better than SMTP. So, today we are going to talk about the differences between those two methods to organize email sending.

Also, here you can see a detailed article about sending emails with help of API and SMTP.

What Is the Difference Between Web API and SMTP Relay?

SMTP is able to transfer emails from one mail server to another and it works like a set of rules. In most cases, the email service providers set up these relay servers and it helps their users to send emails with help of a sender infrastructure.

The Application Programming Interface allows you to integrate different apps. Web APIs and HTTP APIs use the Hyper Text Transfer Protocol for communication. This kind of Web protocol is universal and you can use it for different purposes. In case you want to use it for email sending you will be able to create an app that is able to access the ESPs email handling functions.

What Should I Use: SMTP Relay or Web API?

When you get to choose between SMTP and Web API you should try to do it according to your requirements. Both of these transfer methods are able to send emails at a high rate but their approaches are different. The SMTP requires you to involve the communication between the client and the server which is called back-and-forth communication or the handshake.

Usually, there are lots of these handshakes and this is why the method is referred to as chatty. The SMTP relay is quite simple to use and fits great for casual email senders that require this kind of simplicity for their basic tasks. Also, you can choose this option to integrate with your mail client or CRM system.

On the other hand, the Web API helps you to speed up your email sending process because it requires less back-and-forth connection. Also, its functionality is more extended in comparison with SMTP. It is able to automate transactions, track metrics, etc.

The HTTP API is a common choice for developers with their own products and marketers that have to deal with bulk emails.

TL;DR Comparison Table: Web API or SMTP Relay

Here you can see a comparison table that will show you the differences between these two methods.

SMTP RelayWeb API
Protocol used

 

How it works

SMTP – Simple Mail Transfer Protocol

 

The client and the server communicate using multiple back-and-forths

HTTP – HyperText Transfer Protocol

 

Your app sends HTTP requests to use integrated functions of a third-party service

Pros● Easy to set up

● Platform-independent

● Simpler troubleshooting

● Fast email delivery

● No blockage

● Optimized security

● Analytics capabilities

 

Cons● Slow performance for bulk email

● Changing deliverability of emails

● Possible blockage of port 25

● Complex solution that requires coding skills

● Modifiability

● Unlike SMTP, HTTP API does not have a unique specification, so each email service provider implements its own solution

 

Ease of testingYesNo
Mailtrap applicabilityYesNo
It is the best option for● casual email senders

● integration with a CRM system or mail client

● marketers

● bulk email senders

● app developers

Pros and Cons of SMTP Relay

The SMTP is a protocol that requires your mail user agent to send emails to the SMTP server. So, this email sending method is based on the connection between the server and the client. It performs a TCP connection with a particular port and it is used to send separated pieces of information from the client.

The SMTP Relay Pros:

  • It is easy to set up as the only thing you need to do is to input the SMTP credentials to the mail user agent.
  • The SMTP connection doesn’t require your app or system to follow some kind of restrictions and it is platform-independent.
  • Provides all commands that the client sends to the server with response codes which you can use to investigate any errors or problems.

The SMTP Relay Cons:

  • This method creates multiple connections which potentially increase the number of errors and slow down the sending process for bulk emails. So, SMTP is not a good choice for such emails.
  • Usually, the SMTP relay services use shared IP addresses and it affects the reputation of the sender. Someone might use the same IP address for spam, which definitely will end up blacklisting this IP.
  • Some environments tend to block SMTP because of some firewall limitations. Usually, it happens because of port 25 which is often used for spamming.

Example of Sending an Email via SMTP

Here you will see an example of an email sent via SMTP. For this purpose, we will use the Mailtrap email testing server and the Telnet tool.

>telnet smtp.mailtrap.io 25
<220 mailtrap.io ESMTP ready
>EHLO client
<250-mailtrap.io
<250-SIZE 5242880
<250-PIPELINING
<250-ENHANCEDSTATUSCODES
<250-8BITMIME
<250-DSN
<250-AUTH PLAIN LOGIN CRAM-MD5
<250 STARTTLS
>AUTH LOGIN
<334 VXNlcm5hbWU6
//username encoded in BASE64 OTRiNzg0YjU5NzBlZGY=
>dXNlcm5hbWU=
<334 UGFzc3dvcmQ6
//password encoded in BASE64  MDFhNWQ1MTUwMTFmNmU=
>cGFzc3dvcmQ=
<235 2.0.0 OK
>MAIL FROM:<[email protected]>
<250 2.1.0 Ok
>RCPT TO:<[email protected]>
<250 2.1.0 Ok
>DATA
<354 Go ahead
>From: [email protected]
>Subject: Test email
>To: [email protected] 
>This is a body text 
>.
<250 2.0.0 Ok: queued
>QUIT

If you try to repeat this example you will receive the email in your Demo inbox. So, you don’t have to send your emails to real recipients to test your email sending function.

Pros and Cons of Web API

Web API is an interface that uses web-specific protocols like HTTP for connection. So, it is able to integrate different functions from third-party services into your apps. This method serves as some kind of a bridge to other services or tools.

Web API Pros:

  • This method is good for bulk email delivery as it is faster than SMTP.
  • Web API uses the HTTP protocols which are used to run the world-wide-web. So, it is unlikely that your emails will suffer from any kind of blockage.
  • The API key ensures another level of authentication and provides your account with extra security.
  • Email APIs help you to track different metrics and it helps you to analyze your email sending function.

Web API Cons:

  • You have to use a learning curve for each new API to learn how it is operating. So, it makes this method uneasy to use.
  • The Web API method requires you to have better coding skills as it is a little bit problematic to use in comparison with SMTP.
  • Email APIs receive frequent updates and modifications that may cause some problems and make this method unstable.
  • HTTP APIs don’t have the general email sending protocol, unlike the SMTP relay.

Example of Sending an Email via HTTP API

Here is an example of sending emails with an access token that you will need to generate. Usually, these tokens look like this:

[https://www.example.com/v1/METHOD?access_token=YOUR_API_TOKEN].
$ curl -v -X POST -H "Authorization: $EXAMPLE_API_KEY" \
	--data '{
	"recipients": [
	{
		"address": {
		"email": "[email protected]"
		}
	}
	],
	"content": {
	"text": "This is a test email",
	"subject": "Testing API",
	"from": "[email protected]"
	}
}' https://www.example.com/v1/METHOD?access_token=YOUR_API_TOKEN
**   Trying XX.XX.XXX.XXX...
** Connected to api.example.com (XX.XX.XXX.XXX) port 443 (#0)
** TLS 1.2 connection using TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
** Server certificate: *.example.com
** Server certificate: RapidSSL SHA256 CA - G3
** Server certificate: GeoTrust Global CA
> POST v1/METHOD?access_token=YOUR_API_TOKEN HTTP/1.1
> Host: api.example.com
> User-Agent: curl/7.66.0
> Accept: */*
> Authorization: YSBmYWtlIGFwaSBrZXksIG1hZGUgeW91IGxvb2sh
> Content-Length: 312
> Content-Type: application/x-www-form-urlencoded
>
** upload completely sent off: 312 out of 312 bytes
< HTTP/1.1 200 OK
< Cache-Control: no-cache, no-store
< Content-Type: application/json
< Date: Tue, 17 Sep 2019 13:23:45 GMT
< Server: msys-http
< Vary: Accept
< Content-Length: 109
< Connection: keep-alive
<
** Connection #0 to host api.example.com left intact
{ "results": { "total_rejected_recipients": 0, "total_accepted_recipients": 1, "id": "102364612952283792" } }
}

SMTP Relay vs. Web API – Difference in Email Testing

We already have mentioned our tutorial on how to test the SMTP relay. There you will find a guide on how to connect to the SMTP server and send an email from it.

On the other hand, Web APIs are complex and require you to possess some coding skills to test them. You will likely have problems with testing parameter selection and combination. Also, testing the exception handling function can be problematic as well. If you search for a tool for testing Web APIs we recommend you to try Postman, cURL, and SOAtest.

To Wrap Up

There is no best email transfer method that you can use to create an email sending function. The SMTP is reliable but it can’t deliver your emails at high speed. On the other hand, Web APIs have extended functionality but require you to possess advanced coding skills as this method is more complex.

So, you should try to think about the pros and cons of both methods and choose the one that will be more comfortable and useful for you.

Authored By Manas Singh

He is a continuous blogger and has blogged on different topic. He loves to surf Internet and always trying to get new Idea about new Technology and Innovations and sharing these great information to all the technology lovers.

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