What Is an SMTP Relay [A Brief Crash Course]

Wondering “What is SMTP Relay?” Well, you’re not alone. This article provides a brief crash course on how SMTP relay works. If you’re new to SMTP then don’t worry! We’re going to keep this very high level. Ready? Let’s go!

What is an SMTP Server & How Does It Work? 

Before we delve into what SMTP relay is, let’s start by defining an SMTP server.

SMTP stands for Simple Mail Transfer Protocol. An SMTP server is responsible for delivering outgoing email and it does not accept incoming email. While POP and IMAP are the protocols that allow you to retrieve email from a mail server, SMTP is the protocol that allows you to send email to a mail server.

If you’re looking for, or currently have an email delivery provider to help you send transactional or marketing email, then you might be  familiar with the term SMTP relay service, which is essentially a managed service that helps you send your outgoing mail through SMTP. Most email services today use an SMTP relay service to send email.

What is a Mail Relay?

If SMTP is the protocol for delivering outgoing email, then you can think of mail relay (also referred to as SMTP relay) as the process for transferring an email from one mail server to another.

Consider this simple example:

Imagine that Mike from Company A sends an email message to Tom at Company B.

When Mike sends his outgoing message to Tom, his company’s SMTP Server connects to Tom’s incoming MX server (receiving mailbox), then relays the email over from Mike’s mail server to Tom’s mail server. The image below illustrates the process.

There’s a bit more happening behind the scenes, but this should give you a general idea about how an SMTP relay works.

What’s an SMTP Relay Service?

At the beginning of this post, we explained that SMTP is the protocol for sending outgoing email from one server to another.

And we also revealed that mail relay is the process for transferring an email from one mail server to another.

It just so happens that many businesses need help executing the process of relaying email. This is where an SMTP relay service comes into the picture.

An SMTP relay service (also referred to as an SMTP provider) is a service that helps a sender deliver transactional and bulk email, by routing the email through a trusted 3rd party. The SMTP relay service provides all of the underlying technology and expertise to help businesses deliver email over SMTP.

When should I use an SMTP Relay Service?

Chances are that at one point or another, you have sent an email over an SMTP server.

As discussed above, many businesses use SMTP to send out bulk email, marketing messages, and triggered person to person emails.

Even your favorite software applications probably use SMTP to deliver transactional messages like password resets, order receipts, and other time-critical email like paycheck notifications.

Some common situations when you should send via SMTP mail relay include when:

• You have built a web or mobile app, you can easily “plug in” to an email delivery system so that you can send mail from that app or website.
• You’re looking to simplify email headaches, get your mail flowing again, and improve email deliverability (your ability to reach the inbox).
• You need an easy way to send email from hardware like a printer, scanner, fax machine, or IoT device.
• Your ISP (Gmail) has put a cap on how many SMTP relays it can conduct per day, so you need an SMTP relay provider to help you deliver a higher volume of email without being mislabeled as spam.

Why is using an SMTP Relay Service important?

Email is usually pretty straight forward when you’re sending simple person-to-person email.

However, managing your own email becomes infinitely more complex in situations when you have a web app that sends time-critical notification emails that must reach the inbox. Or when you’re sending mass marketing emails to thousands of recipients at a time.

If you’re sending your transactional and marketing email from your primary mail server like Gmail or Exchange, you’re probably going to experience email deliverability issues, especially as you reach your ISPs maximum daily limits.

An SMTP relay service is the best way to manage batch sends and automated emails. Sending over SMTP through a trusted 3rd party will help you ensure that you don’t experience deliverability issues and that your mail keeps flowing to the inbox without any issues.

How to Start Sending Email Through an SMTP Server?

Your best bet is to use an SMTP relay service like SocketLabs to deliver your email for you.

SocketLabs’ SMTP Services are scalable and easy to get started with. Simply sign up for free and plug your SMTP credentials into your application and start sending.

Want to build your own SMTP server? Here are 5 questions to ask yourself before you DIY >>