SMTP Relay Service Guide – Scalable SMTP Service with Pepipost
Written by
Ayush Verma

Subscribe for updates

SMTP Relay Service Guide – Scalable SMTP Service with Pepipost

Published : March 12, 2020

This Detailed Guide talks about everything that you need to know about SMTP Relay Service. Now you might be a student who is trying to understand what an SMTP Relay is. Or maybe a business who is thinking to pick an SMTP Service but is sceptical on how to do that. With this guide, I have tried to make an attempt to cover everything that you need to know about SMTP Relay and at the same time helping you choose your Next SMTP Relay Service.

Let’s begin, shall we?

If you are into email marketing and want to take a step ahead apart from setting up a contact list and creating a cover letter, then SMTP is a step forward for you.

Now, why do I say that has a very simple answer! The email hosted peer-to-peer via the cloud and access on the web browser at times is not sufficient for mass email programs and campaigns.

Many businesses need to send out bulk emails, automated emails generated from interaction by user and newsletters thus require tailored email solutions. Therefore these services use SMTP to send their emails. SMTP thus can be considered an essential system backend by companies that helps user and company in sending, receiving and relay messages between email senders and receivers.

Also, you might have heard of the term SMTP Relay Service, in case you are looking for an email provider for a newsletter or transactional email delivery.

But why SMTP relay service has become important and how it works?

What is an SMTP Relay?

SMTP (Simple Mail Transfer Protocol) is the default network protocol that has regulated since 1980s the sending and forwarding of the emails on the internet. Though, when you send an email it doesn’t directly go to the mail box of the recipient. This can become inconvenient and dangerous when seen in terms of security.

Instead, sending of e-mails by an external third-party server is made possible. These third-party servers are well-configured smarthost that serves as SMTP relay upstream to handle a large number of messages and at the same time prevent the large volume of spams.

On the Internet, you might find the term “SMTP relay” (or “e-mail relay”) defined in a contradictory way. While some sources speak of it as a process, others describe it as a service. Bringing all the individual aspects together, SMTP relay can be best described as the method of forwarding e-mails from a sender to the recipient on the Internet; and this process is carried out by the so-called SMTP relay servers, that work in accordance with the Simple Mail Transfer Protocol.

Know more about SMTP.

What are SMTP Ports? How to Pick the Right Port as per your needs?

What is a Mail Relay?

The process of transporting an email from one server to the other for delivery is known as Mail Relay. For example, if you want to send an email from your company to someone at other company, then you need to connect to the SMTP server of your company which will then relay your email to the recipient company’s server. Accepting of an email by one server, which is sent by the other server is known as “relaying.”

But in case you are sending an email to a person with same domain in mail address as yours, then it doesn’t involve a second server and so this process of transferring email is not considered as relaying.

What is SMTP Mail Relay?

What is an SMTP Relay Server?

A mail relay server aka SMTP Relay Server is an SMTP server that enables the SMTP relay. So this mail transfer agent accepts all the e-mails from a sender and then forwards them to some third party. In most of the cases, there will be an external third-party server connected between the STMP servers of the sender and recipient.

Everything you need to know about SMTP Relay Server.

What is an SMTP Relay Service?

The message acts like the baton when SMTP relay is considered as the classic foot relay race. An SMTP Relay Service is directed such that it hands off/ transports your message to the other mail server. It acts as a Message Transfer Agent (MTA) trying to make your message reach the intended recipient.

An SMTP relay service is run “in the cloud” just like any other relay service. it receives the message from the server and files it up for delivery to the recipient location. Finally, it delivers the message or in case of unsuccessful delivery, a Non-Delivery Report s generated. In the latter case, the email is said to have bounced and delivered back to the sender. The NDR generated reports the reason behind non-delivery.

How does a Relay Service work?

When you try to send an email or an email service provider sends an email, the email application connects to an SMTP relay or a configured SMTP server. It further communicates through the SMTP protocol. It sends the messages further along with the details and the relay figures out the next step in the journey of the message. The domain name is used by the relay given in the email address, and figures out the destination location where the email needs to be sent. The Domain Name Service (DNS) mainly functions in this step.

After this step, the email is sent directly to the email service of the recipient’s “MDA” (Message Delivery Agent). Or, the mail travels through various Mail Transfer Agents before hitting the recipient’s inbox.

SMTP relays may both be owned and managed by your company, or by Gmail like email provider like Gmail, or by MailChannels.

Learn more about SMTP Relay

Why is SMTP Relay Important?

SMTP Relay service has got its own importance. Usually managing one’s own email server for peer-to-peer email is quite straightforward. This is because such emails are sent only to a limited number of receivers. But, sending of email for a marketing purpose requires tens of thousands of subscribers.  Such emails are not as unique and get mistaken to be labelled as spam. This is the time when SMTP relay provider comes in rescue.

If you send large bulk emails for marketing or jobs using peer-to-peer email service, your delivery rate will suffer and will clog your bandwidth with delay in sending and receiving of the emails. Therefore outsourcing towards SMTP relay service is a convenient way of managing largely automated emails and outgoing email jobs and without any effect on email communications.

Science of Choosing the Right SMTP Relay Service

Functions or Uses of SMTP Relay Service

SMTP Relay service as discussed above hosts some very interesting functions and has got many utilities as discussed here.


SMTP relay server that is properly configured is called as a “smarthost.” It is “smart” because it only forwards an e-mail responsible for either the sender or recipient of the e-mail. And the E-mails that are from the unauthorized parties outside the server are rejected. This is possible by using diverse authentication methods including whitelists, SMTP-After-POP, or ESMTP with the SMTP-Auth extension.

Open mail relay

One of the disadvantages of SMTP is that its basic configuration does not require authentication by any user. If you are not manually adding these mechanisms to an SMTP relay server then it is said to be poorly configured and called as an “open mail relay.” In basic terms it means, the server forwards e-mails without any responsibility for the sender or recipient of the concerned e-mail.

So to effectively solve the problem for spam and security issues with outgoing mail servers it is recommended to rely on the professionally managed SMTP server. In case of Open relay the SMTP server routes messages from both external sources and internal server mail making it more vulnerable to spam abuse.

With SMTP relay, your personal email address becomes irrelevant. Whether you are using Google’s Gmail, Yahoo, AOL, or any custom domain for an email address, simply route your messages via third-party mail server increasing your email marketing by reaching customers without any rate limits or barriers.

Extensions and Upgrades

Extensions and Upgrades to an e-mail system are not implemented right on the sender’s outgoing mail server, but happens through SMTP relay server.

Fighting spam at the sender’s end

It is important for outgoing mail server operators to maintain their reputation online and preventing users from sending viruses, malware and spam. Therefore parallel scanners and firewalls are installed separately on an SMTP relay server against actual mail server.

Backup mail service with the recipient

A smarthost is capable of accepting e-mails for the recipient’s inbox server. This is the case when the recipient cannot be reached at the moment. As soon as the receiver goes online, the smarthost successfully delivers the collected e-mails.

Other Applications

The signing and encryption of e-mails along with the addition of a disclaimer automatically at the end of each text message sent.

E-mail Archiving, Mail routing and rewriting for address changes.

Setting up SMTP Relay

One of the top things about an SMTP relay service is its setup that is easiest. Whether you are working on a WordPress site or a custom domain setting up SMTP Relay is no big deal. All you have to do is simply add and verify your domain name, then make a choice between a dedicated or shared IP address, and finally set up your SMTP relay server.

Now add your username, password, SMTP server hostname, and SMTP port into the application’s configuration settings.

Once everything is done, you can start sending the messages. You can also add SSL connection, depending on the port for an extra layer of security.

Step by Step guide to setting up an SMTP Relay Server

Wrapping Up!

Emailing job sometimes can get tricky like from door delivery to IP blacklisting and other issues. However, with SMTP relay service you can get rid of all these issues. An SMTP relay basically helps businesses and organizations to deliver huge bulks of email without getting them mislabeled as junk or even without creating small sending limits or barriers. It is also possible to send emails using an SMTP server with the aid on an email service providers available online.

Other Related Article.

Check if emails from your domain are landing in Spam – Email Blacklist Tool

Pepipost SMTP V/S Sendgrid SMTP

Unlock unmatched customer experiences,
get started now
Let us show you what's possible with Netcore.
Written By: