Email has steadily evolved from its origins as a research project and academic communications tool, to a wider interpersonal-communications mechanism, to the global linchpin of many types of businesses. The ability to reliably send and receive email is critical to modern businesses that need to communicate with customers, potential customers, business partners, and employees.

Unfortunately, the primary protocol for Internet-based email delivery doesn’t guarantee reliable delivery, meaning that important messages can be—and often are—delayed or lost in transit. This paper will review some of the major factors that can interfere with message deliverability and present solutions that help increase the odds that your important messages will reach their destinations.

SMTP

SMTP The Simple Mail Transfer Protocol (SMTP) has a name that perfectly describes its origin and intended purpose. SMTP was built to be a lightweight, easy-to-implement means to transfer plain-text messages between devices. The original SMTP standard distinguished between a mail transport agent (MTA)—what modern administrators would call a server—and mail user agents (MUA), which most people refer to as clients. SMTP’s goal was to provide a way for two MTAs to pass message traffic back and forth. The protocol doesn’t define any standards for storing messages, giving clients access to them, or carrying complex content types such as audio or image data. It’s just a set of rules for moving a properly structured message from point A to point B.

The first variant of SMTP was designed in a very different environment than what we face today. The original Internet grew from ARPANET, a closed research net- work that was designed for academic and government use. ARPANET and the early implementation of the Internet were designed around the assumption that only a limited number of trusted users would be able to connect to the network, and that commercial traffic wouldn’t be allowed. The competing X.400 protocol was intended to be a more robust message transfer protocol that would be suitable for commercial use; X.400 included features for guaranteed reliable delivery, message tracking, and other security and authentication features—but it was complex to implement, and it ultimately lost out to the simpler, less complex, less expensive SMTP implementations from early vendors.

The version of SMTP that we use today still shows a number of design influences that trace back to its origins:

• The protocol itself didn’t provide for authentication or encryption, which weren’t especially important on a trusted network with trustworthy users. (Since SMTP’s appearance, a series of extensions to the standard have added these features.)
• The ability to get return receipts or delivery notifications is dependent on which client recipients use; servers are required to send delivery status notifications (DSNs) only for messages that are permanently undeliverable.
• There’s no enforced mechanism for classes of service; for example, FedEx and UPS both let you choose from multiple delivery speeds according to how much you’re willing to pay.
• Email filtering often seems capricious, and users have learned through experience that important messages may be filtered arbitrarily by the spam filters in their client, in their server, or somewhere in the cloud. (And now of course, recipients can filter messages within their own inboxes through features like Gmail’s “tabs”.)
• SMTP (or email in general) often falls back to using web-based technologies (i.e. img and anchor tags) to archive click and open tracking metrics.

Conclusion

SMTP was designed in an era when simply storing and retransmitting a message was generally enough to ensure that it was delivered. As the importance of email has grown, and as the number of messages sent across the Internet has skyrocketed, the business value of ensuring that messages are delivered in a deterministic and timely manner has also increased.

Ensuring that your messages are delivered to the correct recipients, on time, requires that you pay attention to the content of your messages, the rate at which you send them, and the path they take between you and the recipients, but the return for this effort can be significant.

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We manage all the technical details, from scaling the infrastructure, to ISP outreach and reputation monitoring, to whitelist services and real-time analytics. We offer world-class deliverability expertise to make sure your emails get delivered, and handle ISP monitoring, DKIM, domain keys, SPF, feedback loops, white labeling, link customization, and more.