Sending emails: How it works in practice

Sending emails: How it works in practice

June 15, 2020



By Eduardo Moschini, software engineer, and Igor Santos, IT infrastructure at :hiperstream

Although some people believed the past decade would bring the end of email communication, the channel is growing in both use and efficiency as more consumers join the digital migration. But successful emailing goes far beyond hitting the send button.

Anyone who has in mind the ease and speed with which we are able to send and receive emails may not imagine - or understand - how complex this process is, especially for businesses delivering a large amount of messages to their customers. Getting to the inbox is a journey, and today we write about what is behind it.

SMTP (Simple Mail Transfer Protocol), the protocol for sending emails, dates from 1982. A surprising age for a technology we still use a lot nowadays. It defines which parameters software must use to communicate with each other - and in the case of SMTP, the parameters for sending and receiving email messages. There is a variety of software to implement SMTP - it’s called MTA (Message Transfer Agent), with Postfix as the most popular OpenSource (it’s the one we often choose at :hiperstream).

Distribution: a large and sophisticated condo

The email protocol was based on the post office system - and we will use this similarity to compare it with delivering correspondence within an apartment complex. When someone sends a letter (or message), it contains the address (name of the service provider) and the complement (user’s name) for delivery. Once there, the postman usually cannot enter the building, so he leaves the parcels at the concierge or with the doorman, and the distribution becomes their task (or of the email provider).

In this scenario, those who choose hosts such as Gmail and Hotmail live in a large condo with sophisticated logistics and security measures. When you choose a provider, you are subject to their policies.

DSN code (and what to do with this information)

Let us make another comparison: while receiving the mail, the doorman returns letters that have something wrong with them - for example, addressed to apartments that don’t exist.

This is no different with emails and the DSN code (Delivery Status Notification - not to be confused with DNS, Domain Name System), that helps identifying why a message returned to the deliver. Looking back at when SMTP protocol was developed, the DSN code is a feature from the 90s. Until then, there was no way to know precisely why an email bounced.

Eventually, there are updates to the SMTP protocol, like this one in 1996 (RFC1892). Now, whenever a delivery is not completed, a code indicates which error has occurred.

Though respecting the criteria established in RFC1892, DSN codes tend to vary from provider to provider. The documentation is very broad and allows providers to use different codes, which often mean the same. For example, the code for non-existent user is 5.1.1 for Gmail, 5.5.0 for Hotmail, and 5.0.0 for Yahoo.

On CCM - Customer Communication Management (:hiperstream’s platform that allows segmentation, sending, monitoring and controlling financial communications), our clients choose how they prefer to access this information, like through the Production Dashboard:


Production Dashboard


Or through the Dynamic Dashboard:


Dynamic Dashboard


It is also possible to consolidate return status in a media file, automatically integrated into the customer's system to feed the database. A common decision is not sending emails for invalid users in the following month.


Communication Library


Submission queue and IP reputation

The email status can also mark "deferred" or "expired". Have in mind that a submission queue is quite common considering the large amount of messages to be delivered by the server. In case the delivery isn’t completed due to a temporary failure, the email isn't discarded, but put back in line for another attempt - which we usually limit to a time frame of up to 48 hours here at :hiperstream.

Another strategy to reduce the queue is using different IP addresses to scale up deliveries, thus increasing speed. To give you an idea, one of our customers uses six IPs for its monthly deliveries.

The most popular email hosts around the world are listed here, and Gmail and Apple are at the top. In Brazil, Gmail and Hotmail usually represent more than 70% of databases, followed by Yahoo!, and others.

Finally, as we've mentioned, whoever chooses a building to live in - or subscribes to an email provider - is subject to its delivery rules. One of the ways the hosts find to protect their users is to verify IP reputation. The score is based on the quality of the submissions, and the metric also includes assertiveness (data validation is key in financial communications), among other criteria.

We use Return Path to check the health of our IP reputation, so we will wrap up mentioning one of their surveys, based on more than 4 trillion email messages: highly reputable senders have 91% of the messages delivered, while the figure drops to 70% - or less - for other senders, usually meaning that the content couldn't pass through the gateway or went to spam.

Do you realize how much is behind emailing - and the importance of the right technology for the strategy to succeed?

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