17 Apr 2019
What Is An SMTP Relay And Why Do We Use It?
17 Apr 2019
If you’re looking to take the next step in your understanding of email marketing, beyond how to set up contact lists and create your first newsletter, then you should probably take a closer look at SMTP.
SMTP stands for Simple Mail Transfer Protocol, and is essentially the backend system that helps you and company send, receive, and relay messages between email senders and receivers.
In an episode of Email Explained, our Sr. Customer Success Manager gives us the 101 of what you need to know about SMTP Relay, but we’ll add a little more depth below.
What is an SMTP Relay?
An SMTP relay is a protocol that allows email to be transmitted through the internet: (1) receiving email from the sender and (2) delivering it to the recipient’s local post office, another SMTP server.
It was first created in 1982 and continues to be the internet standard that is widely used today.
To break this down a bit more, let’s imagine the journey that your normal snail mail may take to get to its destination:
Sending through an SMTP server with an email service provider
So what does this protocol look like when it comes to an email service provider like Mailjet? Businesses that need to send mass email to their customers use SMTP relay for ease of maintenance and added analytics insights.
Sending through an email service provider, like Mailjet, via an SMTP relay saves companies from having to run their own mail server. As you can see in the diagram below, the business or sender creates the email and their server sends it to Mailjet’s SMTP server to prepare and send it out to recipients.
In order to combat spam, a majority of webmail providers (i.e. Gmail, Hotmail, Yahoo, etc.) put a limit on how many emails you can send to different recipients per day. As businesses, who need to communicate en mass with their audience, would often exceed this limit, they will require the services of an enterprise level email sending platform.
An SMTP relay provider can help businesses and organizations deliver large volumes of email without getting them mislabeled as spam or running up against small sending limits.
Email service providers like Mailjet, invest a lot of resources into building their own email infrastructure to handle large volumes and work closely with the major internet service providers (ISPs) and webmail providers to deliver these emails straight to the recipients inbox.
Behind the Scenes: SMTP server tracking
There’s an added layer of value to sending through an email service provider. With Mailjet, before our SMTP servers send an email, our system automatically adds link trackers in the body of your message. This then allows you, as the user, to properly track opens and clicks after an email has been received.
Mailjet also translates feedback from ISPs (Gmail, Yahoo, AOL, etc.), since each one communicates in its own way. Our service saves developers time by converting this into an easily identifiable response, displaying whether an email has either soft bounced or hard bounced.
A soft bounce includes, for instance, when a server is down or full, while a hard bounce is if the recipient’s email address is no longer active or mistyped.
Choosing an SMTP Port
We devote an entire blog to this already, but an important consideration when it comes to SMTP is which port to use.
To understand how ports work, we need to take a step back and see what happens when computers communicate with each other on the internet.
Let’s say you are trying to reach mailjet.com. In this case, the Domain Name System (DNS) is converting this to the actual IP that is hidden behind the name of the site. In Mailjet’s case, this is 126.96.36.199. You probably could remember 4-5 IPs like ours, but who can actually remember more, or really… who would want to?
An SMTP port is one that is meant to be used for SMTP connections. Today, the most common SMTP ports are 25, 465, 587, or 2525. This doesn’t mean that they are the only ones, though. These few ports are the most used ones for these types of connection, and because of that they are almost always opened, which means you should be able to reach your destination.
If you’re looking to decide which port to use, be sure to reach our article on Choosing an SMTP Port to see which one is best for you.
Ultimately, SMTP relay makes our lives as marketers much simpler, by handling all of the heavy lifting in the backend so that we can spend more time crafting content and building out our contact lists.