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How SMTP relay works?
Priya NainNov 25, 2022 7:08:01 AM5 min read

SMTP Relay: How Does It Work, and Its Top 5 Benefits

Sending an email seems like an easy job. You draft the perfect message and hope to hear from the customer.

But did the email even go through the receiver’s inbox?

Unless you are a tech geek or frustrated with poor customer response, chances are you might not even care what is going on in the backend. And this can prove to be a disaster for your email marketing optimization.

Before you get scared of the technicalities and switch over to a funny cat video, scroll down.

In this article, we will break down SMTP relay so that even your five-year-old can understand it easily.

Via Giphy

Wait…What is an Email Relay?

An email relay is the transmission of an email message to someone through email servers.

Let’s understand this with an analogy. In old times when people sent mail, they first dropped it to their post office, from where it gets delivered to the receiver’s post office. This travel of messages from one point (server in this case) to another is called a relay.


What is SMTP?

SMTP, or Simple Mail Transfer Protocol, is a set of rules defined for sending emails from one sender’s email server to the recipient’s server.

Carrying forward our analogy, SMTP is the postman who picks up the mail from the post offices and delivers it to the right person.

But SMTP is only responsible for sending mail. It is not involved in accepting incoming emails.

How Does SMTP Really Work?

Before exploring the process step-by-step, let’s see the overview first.

First, the sender prepares the message with the details of the receiver. A verification request is sent to the addresses of the sender and receiver. Once they are verified for accuracy, the message is transferred from the sender to the receiver.

Now, here is the nitty-gritty of the process.

  1. The Mail User Agent (MUA) is the sender’s email client (Gmail, Yahoo, etc.). It submits an email to the Mail Submission Agent (MSA), which checks the email for any error.
  2. If the details are correct, it transfers the email to the Mail Transfer Agent (MTA), which checks the recipient’s email address for accuracy.
  3. MTA uses the MX (Mail Exchanger) record to verify if the sender’s domain is authenticated and approved for sending a message to the recipient.
  4. The Mail Delivery Agent (MDA) delivers the message based on the address's accuracy.

The SMTP model has two types.

  1. Store and Forward: It sends emails to recipients whose address is part of the same domain family. For example, colleagues of an organization with the domain name
  2. End to End: It is used to send emails to a recipient who is part of another mail server and domain. It is especially helpful if you are sending transactional emails to your customers based on their action triggers

What is SMTP Server?



Any server that receives, manages, and transfers emails using the SMTP protocols is called an SMTP server.

There are mainly two types of SMTP servers.

  1. Regular Server: It’s the server that handles the daily emails sent for personal communication. Email providers like Gmail, Yahoo, and Outlook have this type of server implemented for use. These have strict limits on how many emails you can send in a day.
  2. Dedicated Server: Since regular servers have a limit set to them, dedicated servers are used for bulk communication by organizations.

What are the Benefits of Using an SMTP Server?

1. Engage Quickly & Effectively

When you send messages through a peer-to-peer email service, you risk your email deliverability. It is because these are not made to allow bulk email communication

from an email address due to potential spam.

An SMTP relay server delivers a large volume of messages, making your bulk communication easier.

2. Compliance on Auto-pilot

If your business communication doesn’t let subscribers opt out or manage their preferences, you risk GDPR complaints. And these can cost you not just money but the sender's reputation.

SMTP servers, by default, add the unsubscribe and preference feature to let users take necessary action, reducing your risk substantially.

3. Talk With Numbers

With a peer-to-peer email service, you can send a message easily. But has that email even reached the subscriber’s inbox? That’s the million-dollar question.

SMTP servers allow you to identify which users got your email and whether they have read it or not.

Such statistics are a surefire way to analyze your email marketing strategy and make relevant improvements. 

4. Review First, Then Ship

Your email might land differently than you see it on your system screen. And even a slight issue with alignment or font is enough to tank your efforts.

To avoid people passing your email as spam, convey your message effectively with visual appeal. SMTP servers let you review your marketing emails via an intermediate interface before sending them to the customer.

5. Reduce Road Blocks

SMTP email servers are designed to send messages across the internet without raising any red flags from MSA.

It’s a big win when you deal with bulk messages, and time is critical to bring in new leads and revenue.

Is it Smart to Set Up Your Own Local SMTP Server?

Seeing all these benefits, it would make sense to set up and run your own SMTP server.

But let’s look closely.

Though a local SMTP server will offer you limitless outgoing emails with complete control, configuring it is not an easy feat. It will demand your significant time and resources. The bounce rate might also increase up to 30%.

That’s where a reliable SMTP relay service steals the show. It is an affordable solution to enjoy all the benefits and more.

SendPost offers an SMTP relay through which you can connect and deliver within minutes. It also powers up your email marketing efforts with accurate and real-time deliverability statistics. That means complete transparency of your operations. While dedicated IPs boost your email deliverability, custom alerts let you manage and control your processes.

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Priya Nain

A writer, content marketer, and editor with 4+ years of experience helping SaaS companies get users, and engage them. Nice girl, rarely mean.