LACNIC Blog | MX Records: The Untold Story of Email
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LACNIC Blog > DNS > MX Records: The Untold Story of Email<br>MX Records: The Untold Story of Email<br>March 25, 2025<br>Designed by MagnificBy Alejandro Acosta, R+D Coordinator at LACNIC<br>Advances occur across the world of technology, and DNS and email are no exceptions. In this blog post, we’ll go back in time and explore the history behind certain DNS records, we’ll briefly examine how email systems worked before 1983, and we’ll acknowledge the powerful MX record, which revolutionized how email is handled on the Internet. It should be noted that we won’t use the concepts of MTA (Mail Transfer Agent) or MUA (Mail User Agent), as these mnemonics were introduced years after the MX record itself.<br>Email was very different back then from what we know today.<br>1. Early email systems appeared in the 1960s and 1970s, developed at universities and research centers. One of the first was MIT’s ‘CTSS Mail’ program, which allowed users to send messages to others, but *only* on the same server.<br>2. Formats and Protocols (1971-1982). At this time, there was no standardized protocol for email. Instead, each system used its own format and methods for sending and receiving messages. This meant that messages sent from one system to another might not be compatible.<br>Continue reading<br>(Free access, no subscription required)<br>3. Ray Tomlinson’s work in 1971 made history by implementing the first email system capable of sending messages between different computers on the ARPANET. Tomlinson introduced the use of the ‘@’ symbol to separate the username from the hostname, a format still in use today. Fun fact: There are many stories about why the ‘@’ symbol was chosen to separate the username and hostname. Part of the reason is because ‘@’ is read as ‘at,’ meaning that luisalfonso@lacnic.net is read as Luis Alfonso at lacnic.net<br>4. In 1983, the introduction of SMTP (Simple Mail Transfer Protocol) established a standard that allowed more efficient and universal communication between different email systems, ushering in a new era in digital messaging.<br>Which DNS records were used before MX?<br>Before MX records were introduced, MD (Mail Delivery) and MF (Mail Forwarding) records were used to connect mail agents in the Domain Name System (DNS). The original specification used these MD and MF records to connect mail agents.
3. Ray Tomlinson’s work in 1971 made history by implementing the first email system capable of sending messages between different computers on the ARPANET. Tomlinson introduced the use of the ‘@’ symbol to separate the username from the hostname, a format still in use today. Fun fact: There are many stories about why the ‘@’ symbol was chosen to separate the username and hostname. Part of the reason is because ‘@’ is read as ‘at,’ meaning that luisalfonso@lacnic.net is read as Luis Alfonso at lacnic.net<br>4. In 1983, the introduction of SMTP (Simple Mail Transfer Protocol) established a standard that allowed more efficient and universal communication between different email systems, ushering in a new era in digital messaging.<br>Which DNS records were used before MX?<br>Before MX records were introduced, MD (Mail Delivery) and MF (Mail Forwarding) records were used to connect mail agents in the Domain Name System (DNS). The original specification used these MD and MF records to connect mail agents.<br>Key aspects of MD and MF records:<br>MAILA queries requested both MD and MF records.<br>MD records identified hosts that were expected to have the recipient’s mailbox.<br>MF records identified hosts that were expected to act as intermediaries and forward mail to the final destination.<br>The problem with using separate MD and MF records was that a mail agent performing a MAILA query couldn’t effectively use the cache, as this could only store results for either an MD or an MF query, but not both. The solution was to replace MD and MF with a new type of record —the MX record— which combines information from MD and MF records into a single type.<br>F.ISI.ARPA A IN 10.2.0.52
F.ISI.ARPA MD IN F.ISI.ARPA
XXXX.ARPA CNAME IN F.ISI.ARPA
XXXX.ARPA MF IN A.ISI.ARPAExample configuration excerpt taken from RFC 882.<br>What are DNS MAILA queries?<br>MAILA queries were DNS queries used to retrieve both MD and MF records from the Domain Name System.<br>Key aspects of MAILA queries:<br>They requested both types of records, MD and MF.<br>MD records identified hosts that were expected to have the recipient’s mailbox.<br>MF records specified hosts that were expected to act as intermediaries.<br>However, using separate records presented a caching problem. Since a mail agent couldn’t rely on the cache having both records, it often had to query the authoritative servers directly. To solve this issue, MX records were introduced, which combine the information into a single record type.<br>Example of a DNS MAILA query<br>Example of a DNS MAILA response<br>Additional reading:
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