by Ryan Ozawa
Article filed in
What is a smart host?
by Ryan Ozawa
Back in the early, idealistic days of the Internet, sending an email was one of the most basic activities users could perform, and the entire system was designed to make it as easy as possible.
It didn’t take long before schemers and scammers spotted an opportunity to make money, and email inboxes were flooded with spam. One of the first measures put in place to stem the tide of junk email was the implementation of smart hosts.
When the net was young
In the 1970s, individual computers connected directly with each other over the Internet. These computers were largely used by researchers, academics, and military facilities, so the number of connections was manageable and the people using them largely trusted each other.
As the number of users and connected computers exploded, the architects of the Internet implemented the Simple Mail Transfer Protocol (SMTP) in 1982. SMTP established the protocol through which electronic mail messages are sent and received. And SMTP still serves as the foundation of the way email is handled today, nearly four decades later.
One of the earliest challenges to be solved with email was maintaining a centralized address book of where messages should be sent. This was before the development of the domain name system (DNS) and MX records for email routing. Because it was impossible for each individual connected computer to find every other computer, Internet architects established open mail relays.
An open mail relay was a centralized server designated specifically to receive and forward email messages. Any Internet user could point their email application at one of these servers, and their messages would be forwarded on to their destination—often through other open email servers.
Evolution of the smart host
These open mail relays were called smart hosts (or smarthosts) because they were smarter about mail routing than a basic terminal or connected computer. They did the hard work of sorting out the best route for an email message to its destination, so individual machines didn’t have to maintain their own directories and network maps.
Smart hosts were set up as a public service. But when spam, or unsolicited commercial email, started to overwhelm the system, open mail relays quickly became part of the problem.
Pretty soon, having a mail server available for redelivery of mail to and from everyone came to be seen as a public menace,” wrote Rick Moen in the June 2005 issue of the Linux Gazette. “Like having an unfenced swimming pool in a neighbourhood full of children.”
The modern smart host
Smart host operators had to quickly adapt to the new, spam-infested reality, as open mail relays were soon being blocked by other Internet servers. Efforts to better manage email routing were accelerated in 2003 with the passage of the Controlling the Assault of Non-Solicited Pornography And Marketing (CAN-SPAM) Act in the United States.
As a result, the term smart host evolved to describe an email server that was not an open mail relay. Today, a smart host has several protections in place to prevent spammers and scammers from abusing it.
What does a smart host do?
A smart host is a critical component of any operation that requires sending large volumes of email messages. The services a smart host provides include:
- Requiring authentication to send email messages (unlike an open mail relay)
- Providing much higher hourly or daily limits on the number of email messages sent (compared to typical ISPs)
- Maintaining a good email sender reputation (avoiding blocklists and the need for IP warming)
- Email filtering and attachment scanning for viruses, malicious scripts, email phishing and other threats
Not all smart hosts offer the same features and protections, however.
Paubox is a smart host, providing seamless and secure HIPAA compliant email that can be composed and sent directly from your existing email client (such as Google Workspace or Microsoft 365) or through the Paubox Email API. Our solution is HITRUST CSF certified and a smart choice for healthcare businesses.