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What happens when you press send: the anatomy of an email

What happens when you press send: the anatomy of an email

By Jonathan Rodger, founder of email marketing provider, Message Horizon.

It is estimated that around 250 billion emails are sent each day, making the global email community bigger than any single country in the world. So many businesses are now totally reliant on email, whether for marketing purposes or simple communication, yet for most users the actual mechanics of how an email actually works are still a mystery.

For a marketer, knowing how an email is constructed and verified are important factors in determining the success of an email campaign. Understanding the limitations of its delivery system can also help with managing expectations of what is possible with email tracking

The basic format of an email hasn't changed much since Simple Mail Transfer Protocol (SMTP) was released in 1982. Whilst its creators can't possibly have imagined the explosion in its usage in the decades to come, it has stood the test of time well.  Whether it is an email used in a marketing campaign, or a one-off mail sent from Outlook, the construction of the email is basically the same.

So what happens when you press “Send”?

First, your email software converts your message into the email format. It then attempts to connect to the SMTP server defined in your email account settings. If you use a web-based email service this will be configured by the company running the service.  

The SMTP server will interrogate a Domain Name System (DNS) server to look up the exact location of the server that is responsible for handling incoming emails for the domain that you are sending to. This is referred to as the Mail Exchange server.

Once identified, your ISP's SMTP server will connect to the recipient's mail server and attempt to deliver the complete message. If successful, the recipient's mail server will look at the email alias, i.e. the part before the @ sign, and based on this will store the email for the recipient to download as soon as his email client software connects to his ISP.

The effect of spam

The sheer volume of unsolicited emails was never anticipated when email was first designed, so a few initiatives have been put in place to allow mail servers to verify that emails received are genuinely from the actual organisation named in the headers.

Sender Policy Framework (SPF) is now widely used to verify that the sending domain is authorised to send from the SMTP server it originates from. This can of course be abused by spammers if they own a domain with SPF enabled for the mail servers they use; however this makes them easier to trace.

Who bears the cost?

As with most things performed over the internet, the use of email is technically free of charge to the sender and the recipient. In the case of free web-based email services such as Gmail and Hotmail the cost of sending and receiving email is borne entirely by the service provider. The considerable infrastructure and bandwidth required to manage huge volumes of email for these services is funded by advertising.

Some years ago large ISPs such as AOL and Yahoo raised the prospect of charging businesses a small fee per email to guarantee delivery of marketing emails to their recipients. Such schemes were pulled however due to large numbers of protests against the creation of a “two-tier” email system.

How secure is email?

Email is not designed to protect content, it is an open and unencrypted format. Emails can be stored at various points along their journey on networks and servers not within the sender's control, and often for months.  

Problems with tracking of emails sent

In theory, SMTP should provide notification of whether an email has been received or rejected by the recipient's ISP and it issues a bounce message if a message isn’t accepted. However, this notification procedure is not foolproof and bounce messages can fail due to network or system failures. Bounce messages are often disabled by ISPs as a deterrent to spammers, who can use them to determine whether a user exists or not. If no bounce message is received and the email is not actually opened, it is impossible to determine whether the email was actually delivered.


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