SMTP Relay Service

SMTP Relay Service [A Complete Guide]


This tutorial is a complete guide where you will learn all about SMTP Relay. Gmail, Yahoo, Outlook or any of your internal corporate mail servers are good to deliver 1-1 personal emails. But, all of these services will fail when you want to send emails at scale, say to millions of users. To deliver emails at scale, you need to understand the concept of SMTP and its implementation. Whether transactional emails, newsletters, automated alerts or notifications, you can send everything using an SMTP relay service.

Let’s first understand what SMTP is?

What is SMTP (Simple mail transfer protocol)?

SMTP is a standard mail protocol to deliver emails to its destination. Whether you’re sending a 1-1 or a bulk announcement email, both use SMTP at the backend to exchange emails between the servers.

Functions to generate email

While SMTP is best at its core job of exchanging emails, but you can’t use it for composing your emails. “Email Composing” is another job, which ensures the data packet generated by the sender, is understandable by the standard SMTP. Almost every programming language has its inbuilt function to create SMTP-understandable email data packets. Here are a few examples of functions to generate emails:

  • PHP –> mail()
  • Python –> smtplib
  • Perl –> mail
  • Java –> JavaMail API

When you use Outlook, Thunderbird or any other mail client, then they uses some of these functions only to generate the email data packet. Once the SMTP-understandable data packet is ready, you need to submit the same to a SMTP server for doing the mail relay.

What is Mail Relay?

Mail Relay is a process of transferring the raw mail packet from one server to another for delivering your email. There may be one or multiple servers involved during this entire journey of mail relay. For example, if you’re sending a mail from your corporate email account to a prospect’s Gmail account. Then, in that case your corporate server will be connecting to Gmail’s MX server to relay the email.

On the other hand, if you’re sending email internally to one of your fellow employees. Then, in that case, it will be an internal relay as your mail server will not be connecting to any external server. It will be just doing an internal routing on the email between two accounts.

What is SMTP Relay Service?

SMTP Relay is a service, which routes the email data packets through an external SMTP server. This external SMTP server will be responsible for the delivery of your emails.

SMTP relay service is easily pluggable with your code or application to deliver your real-time transactional emails like Signup Confirmation, Forgot Password or even the bulk marketing emails too.

Choosing a good SMTP relay is very important to ensure the secure and timely delivery of your emails. There are primarily two types of SMTP Relay Service, which can be further classified based on its licensing:

  1. Inhouse SMTP Relay
    • Open Source
    • Commercial
  2. Cloud SMTP Relay Service (Mostly commercial with some free sending limits)

What is In-house SMTP Relay?

In-house SMTP Relay is a self-hosted service to route emails to its destination server over the internet. You can setup an inhouse SMTP relay service by installing an MTA.

A Mail Transfer Agent (MTA) or mail relay is a software that has all the SMTP libraries in-built, to relay emails. It also controls all sorts of error handling over the network. Both open-source and commercial MTAs are available in the market. Postfix and SendMail are two of the popular open-source MTAs.

How will Inhouse SMTP Relay work?

In-house SMTP relay acts as a common mail relay service for all of your projects and applications. Few examples on how in-house smtp relay can be helpful:

  1. Internal CRMs can connect to this common relay to deliver bulk or 1-1 email communication to users. 
  2. Mail clients like thunderbird or outlook can connect to this organisation-wide common relay service to transmit the email data packets to the receiver.

Using an In-house SMTP relays is best when you don’t want to share data to third party. But, it has its own cons when it comes to scaling and ensuring high inbox delivery rates for your emails. Most common reasons for your in-house SMTP relay emails going in spam are:

  1. Sending IP address is blacklisted or carrying low reputation on various anti-spam engines.
  2. Email authentication mechanisms like SPF and DKIM are not implemented. SPF and DKIM are the two email authentication mechanism to ensure that emails are not getting forged or tampered on its way. You need to install both of these authentication frameworks to ensure all your emails are complying with the global best practices for email.

Another critical point to consider is the setting of the right sending IP address on your SMTP Relay server. It would be best to use various monitoring tools to track the reputation of these sending IP addresses. This is required to ensure your emails are not hitting the spam folders of the recipient.

Constantly monitoring and tweaking the configuration of your mail relay server can be an expensive and very challenging effort.

The efforts will be even worst when you don’t have the internal email expertise.

If your email volume is in few hundreds, then go ahead with any of the good in-house SMTP relays. But, if you’re looking for scale, then using an inhouse relay solution will be a nightmare.

What is Cloud SMTP Relay Service?

Cloud SMTP relay is a third-party relay service to route your emails to its destination. As this is a third-party service, so you don’t have to install any MTA on your server. Just connect to this cloud service using SMTP/API. The email service provider will be handling all sorts of email delivery related issues. Using a cloud relay will help you focus more time on your core business.

How will Cloud SMTP Relay Service work?

In the case of cloud SMTP, your project or application like Outlook will be connecting to a remote relay server to deliver emails.

In case of in-house setup, you have to worry about the complete email delivery infrastructure. On the other hand, in the case of cloud SMTP relay providers like Mail250, every aspect of email delivery is covered by the email provider.

You will be having more time focusing on your core business instead of worrying about the actual delivery of emails.

Mail250 SMTP Relay Service

Mail250 is a cloud SMTP relay service or MTA ready to meet the growing email sending needs of your business. Mail250’s SMTP relay has built-in i-MTA.

AI-driven Mail Transferring Agent (i-MTA) is a MTA which keeps itself updated with the recent anti-spam policies and user behaviors. This intelligence enables smart delivery for your emails.

Whether you’re looking to deliver your critical transactional emails or the marketing newsletter, the SMTP relay has support for both. It can ensure the emails are reaching on-time without having you worried about the setup and monitoring.

Mail250’s SMTP relay offers extensive email delivery reports to track each of your emails: 

  • Whether the emails are getting delivered or getting bounced?
  • Whether the user has opened your email or not?
  • Which of the users are not interested anymore in receiving email communications?
  • What is the best time to send emails? And so on.

You can analyse all of the above metrics to build on your next email campaigns.

Hope now, you got an idea about SMTP Relay Service, and why it is important to choose a right provider for your business.

Previous Post
Spam Trigger Words to Avoid in Your Email Content
Next Post
Email marketing best practice tips (A to Z of Email Marketing)

Related Posts