Reading Time: 3 minutes(Last Updated On: June 26, 2019)

No matter the purpose or intent, Email delivery plays a crucial role in our daily lives. SMTP Server allows the delivery of a personal email you sent to your friend Jane or that email campaign for your eCommerce store/business.

Globally an impressive 269 billion emails are sent/received each day and there currently over 3.7 billion email users worldwide according to stats from Radicati.

What is an SMTP Server Relay? You may ask…

What is an SMTP Server Relay?

SMTP stands for Simple Mail Transfer Protocol, This is the protocol that allows you to send an email.

What are mail Relays? a mail relay or SMTP is an email server, a device and/or program which routes/redirects/directs email to its correct destination. So there you have it, a mail relay or SMTP is an email server, a device and/or program which routes/redirects/directs email to its correct destination.

Your typical mail relay tends to be used within local networks to transmit emails among local users such as all the students/faculty email addresses of a college campus. They play a crucial part in email aliasing where multiple email addresses are used but the mail relay forwards all the traffic/messages to the specific email addressed to one single address.

A mail relay is different from an open replay which is an email server which processes a mail message that neither originates or ends with a user that is within the server’s local domain (i.e., local IP range).

How do SMTP Relays Work?

A user typically signs up for an email address from a free email provider. These email providers allow the user to use the free email providers domain and thus also their email servers.

Some popular free email providers include [email protected], [email protected], Yahoo [email protected], [email protected] and [email protected] just to name a few.

Using the email providers webmail service allows you to both send and receive an email. The interface even allows you to handle the email server settings that handle redirecting your incoming and outgoing emails.

SMTP Server Relays - What They Are and How They Work 1
Photo by Host Sorter on Unsplash

Apps such as Microsoft’s Outlook, Apple Mail or Mozilla Thunderbird which can be found on various platforms are known as local clients. They allow you to input your email providers incoming and outgoing mail server settings when you setup the local client.

Incoming server settings tell the email client where it can fetch your email from while the outgoing settings tell the email client which email server it can send your email to.

Outgoing server setting is also knows as a SMTP server settings.

Seriously How do they work? What is an SMTP’s roles in the email sending process?

angry youve got mail GIF

Look us look at the average email scenario that you are Marie need to send an email to Harry.

Here is Marie, Here email address is at [email protected]

Although Marie is using Yahoo, she likes to use Microsoft Outlook email client to create, read and send her emails.

To ensure her email client could send, receive and read emails, she entered Yahoo’s email server settings when she configured the local client.

So she writes a new email to her friend Harry who uses Gmail within the MS Outlook client from here Windows PC.

When she clicks send, The client sends Harry’s address, Marie’s address and the body of the message she has created to Yahoos SMTP servers.

Once received, the Yahoo STMP server breaks Harry’s email address into two parts:

  • The Recipent ID which is found infront of the at sign
  • and the domain name, which in this case is GMail.com, shown after the at sign

The Yahoo SMTP server then goes out to the internet and through a series of server conversations, locates the SMTP server for the Gmail domain.

The Yahoo SMTP server then passes Marie’s email to the GMail SMTP server.

email GIF by Capitol Records

Once it arrives at GMails SMTP server, it remains there until Harry logs into her Gmail account and retrieves the email.

So SMTP is the message sending protocol which makes sending and receiving and email possible. It allows you to send your email from a email client to a email server.


In conclusion, an email server relays OR outbound SMTP ensures your email to be sent to its respective email server to the next.

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