Email (email, RFC Style Guide) is undoubtedly one of the cornerstones of the Internet. Before email, the Internet was merely a network for researchers to synchronize technical information; email largely brought a breath of life to the Internet. Today, as various Instant Messaging (IM) technologies mature, the casual conversations that once filled our lives through email are gradually fading, yet we can still gain some insights.
The author is not very knowledgeable and has limited energy; if there are any omissions, please feel free to criticize and correct.
Communication on the Same System#
Today, email is often seen as one of the earliest decentralized messaging networks, allowing users to communicate across servers. However, its predecessor was confined to the host, used only for communication between different users on time-sharing systems. MIT's CTSS system is a typical example.
┌───────┐ ┌───────┐
│ User ├─────────┐ ┌────────┤ User │
└───────┘ ┌──────┴─┴─────┐ └───────┘
│ Shared │
│ File(s) │
├──────────────┤
│ Time-sharing │
│ Mainframe │
┌───────┐ └──────┬─┬─────┘ ┌───────┐
│ User ├─────────┘ └────────┤ User │
└───────┘ └───────┘
The above diagram illustrates a popular implementation at the time, which involved sharing a file among multiple users on the same mainframe to convey information. This method of communication later evolved into the precursor of email—a mail system on a single system. Even today, host-bound email still exists and is widely used in scenarios requiring message notifications, such as internal system alerts. In these scenarios, emails that are transmitted solely within the system can be easily deployed (as the technology is mature, and many systems even come with corresponding solutions), without incurring additional costs.
In fact, developers on both mainframes and minicomputers during the same period created various software for communication within the same system. Some of these required both sender and receiver to be online simultaneously, evolving into today's instant messaging, while others are closely related to today's email. However, at that time, they were mostly incompatible with each other. These inventions predated the birth of the Internet, and computer systems largely operated independently. The ability for users on one device to communicate with each other was already satisfactory. By the 1970s, computers began to be commercially applied, leading to the emergence of many commercial email formats for internal office communication.
Entering ARPANET#
The predecessor of the Internet is ARPANET, which marked the beginning of email's cross-system transmission. In 1971, Raymond Tomlinson sent the world's first true email, using a new version of existing software called SNDMSG, which allowed information to be transmitted in file form across networks. Through ARPANET, this email was unprecedentedly sent from one host to another, ushering in the era of network communication. It also introduced the @ symbol for indicating the host to which a user belongs. This symbol is now widely used in various contexts to represent accounts on social platforms.
┌──────┐
│ User ├─────┐
└──────┘ │
│
┌────┴───┐
│ │
┌──────┐ │ Host ├─────────┐
│ User ├──────┤ │ │
└──────┘ └────────┘ ┌────┴──────┐
│ ARPANET │
┌────────┐ └────┬──────┘
│ │ │
│ Host ├─────────┘
│ │
┌──────┐ └─┬──┬───┘
│ User ├────────┘ │
└──────┘ │
│
│
┌──────┬─────┘
│ User │
└──────┘
At this time, email was sent via the NCP protocol, marking its first combination with a true protocol. NCP was soon replaced by TCP, and email systems gradually matured as a result.
┌──────────┐ xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx ┌──────────┐
│ Host │ x x │ Host │
│ │ x x │ │
│ │ x x │ │
│ │ x x │ │
│ │ x x │ │
│ │ x ┌───────────────────────┐ x │ │
│ │ x │ Network Applications │ Email... x │ │
│ │ x ┌────└───────────────────────┘────┐Higher-level x │ │
│ ┌───────┐ x │ Application Protocol │ x ├───────┐ │
│ │ NCP │ x ├─────────────────────────────────┤ x │ NCP │ │
│ │ ├──x─┤ Interface ┼─────────────x───┤ │ │
│ └───────┘ x │ Network Control Protocol │ x ├───────┘ │
│ │ x └─────────────────────────────────┘ x │ │
│ │ x ▲ x │ │
│ │ x │ x │ │
│ │ x │ x │ │
│ │ x │ x │ │
│ │ x Protocol x │ │
└──────────┘ x Layering x └──────────┘
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
The Birth of Many Familiar Protocols...#
Subsequently, many familiar protocols emerged, such as SMTP, IMAP, and POP, as well as some proprietary protocols like Exchange. SMTP is undoubtedly the universal solution for any field involving cross-server communication. It is precisely because of universal protocols like SMTP that today's email largely retains its decentralized nature.
┌───────────────────┐
│User: │
│[email protected]│
└────────┬──────────┘
│
Webmail
│
┌────────────┐ ┌─────┴──────┐
│ │ │ │
┌────────────────────────────────────┐ │ │ │ │
│ From: [email protected] │ │ │ │ │
│ To: [email protected] │ │ Port 25├─────────────────────►│ │
│ Subject: Body: ... │ │ │ SMTP │ │
└────────────────────────────────────┘ │ │ ─────────────────── │ │
│ │ TLS(Encryption) │ │
┌───────────────────┐ │ │ ─────────────────── │ │
│User: │ │ │ TCP │ │
│[email protected]│ │ │◄─────────────────────┤Port 25 │
└──┬───▲────────────┘ │ │ │ │
│ └───────IMAP/POP────────┤ │ │ │
│ │example.com │ │example.net │
└───────SMTP───────────────►│ Host │ │ Host │
└────────────┘ └────────────┘
Webmail allows users to view emails in a browser, using web protocols (such as HTTP(s)) to retrieve emails from servers. Today, the vast majority of email service providers offer webmail services and encourage users to utilize them. Some providers that claim to prioritize privacy even avoid offering traditional protocol services (IMAP/POP, client SMTP) and only provide more modern webmail to mitigate risks associated with outdated protocols. However, critics argue that this practice leads to greater user dependence on a single platform, losing the portability of standard email protocols and weakening the decentralized nature of email systems. Others believe that webmail interfaces can be made more attractive or provide email service providers with more opportunities to collect user information.
Today, we have many well-known decentralized instant messaging standards. The most famous are probably XMPP and Matrix. Many open-source projects have replaced the similarly dated IRC with them. They actually adopt a similar idea to email, where users belong to different hosts, and both host-user and host-host communications use a universally applicable set of standards. During the era when IMAP, POP, and SMTP were born, there was no data format like JSON that possessed both machine-readable and human-readable characteristics. Now, driven by JSON, cross-system communication has become effortless.
Open Source, Encryption, and Asynchronous Revitalization of Email#
We say that many open-source projects have replaced email writing with online forums and decentralized instant messaging standards, yet large open-source projects like Chromium and the Linux Kernel still use mailing lists. Many might think that using this as evidence to assert that mailing lists (email) are still not outdated is overly stubborn, and mistakenly believe that these projects refuse to switch collaboration methods simply because migration incurs costs. In fact, even today, mailing lists still outperform online forums and chat rooms (even decentralized chat protocols). Please allow me to share my perspective on why I believe the open-source community, encryption, and the concept of asynchronicity have revitalized email.
First, deploying a mailing list is very simple. For users who are proficient, setting up a mailing list service can be accomplished with just a few commands, while deploying an online forum may require extensive configuration. As traffic increases, it can also incur high costs. For many open-source projects, funding is tight, so they naturally choose to stick with the mailing list collaboration model, especially since everyone has already adapted to it. Simplicity also brings stability, which is why some large projects choose to continue using mailing lists; it is a familiar way for their developers and users to communicate and report issues, and the principle is very simple—it's just mass emailing. Thus, even when collaboration workflows encounter issues due to high traffic, it is easy to pinpoint the individual at fault. In contrast, web-based forums and collaboration based on rapidly evolving chat protocols may face more complex architectures and harder-to-locate problems. Sometimes, complexity can even introduce security risks that directly threaten the infrastructure of the entire project.
Second, email provides comfort to individuals participating in projects. Most open-source projects are driven by volunteers; volunteers cannot serve the project around the clock, as they have their own lives to consider. Online forums require constant refreshing, and the "read" feature of instant messaging, along with the expectation of short, conversational replies, can create a sense of pressure to "respond immediately." Only email offers the right level of reminder intensity: it alerts you that there is an email but also gives you the opportunity to think carefully or ignore it. Personally, I feel that if an instant message is sent to someone and there is no response, it may seem impolite; however, if it is an email, the situation may be entirely different: if the other party does not reply, they might be considering whether their wording was inappropriate. This may be because, as a more formal medium, email inherently carries more respect and offers more options. Volunteers undoubtedly need respect; they participate in activities out of interest and should have the right to control their level of involvement. If it were a commercial company or individuals/groups employed to contribute to an open-source project, timely responses to their clients would be a professional requirement. However, for most volunteers, email is a way to respect each other's time.
Respect for time is not only reflected in the relaxed atmosphere of email but also in some functional characteristics that may be equally useful to commercial entities. Email has a natural asynchronous property, allowing multiple transactions to occur concurrently. In a traditional chat room, various topics can flood the dialogue box, and if there are interruptions, it can become chaotic. Certainly, modern chat clients have methods like "threads" to address this issue, but these methods may also have been inspired by email. In email, different topics can be laid out simultaneously, and each can be assigned its own priority. The subject line provides a brief description of the issue, allowing participants to quickly see the most valuable questions, and opinions from various sources can be categorized and summarized. The body of an email is clearly longer than an instant message, making email a tool that promotes thought. Writers realize they need to accurately describe the problem, which helps them organize their thoughts; this process itself aids in problem-solving and clarifying their minds. Compared to conversational communication, this type of exchange is actually more efficient and respects each other's time. Additionally, after years of development, most email clients can appropriately integrate with encryption technologies like OpenPGP to ensure secure communication.
In addition to all of the above, email is also widely compatible with various operating systems and devices, adaptable to various working conditions, and can help protect privacy (generally, the IP addresses of both sending and receiving parties are not disclosed to each other, let alone technologies like cookies). However, if today's email systems do not continue to evolve technologically, this hard-won masterpiece may also be forgotten. Currently, many new extensions for email have emerged, such as email security services like DKIM, protocol redefinitions like JMAP, and enhanced encryption solutions like lacre.
Perhaps the future of email can still exist as a cornerstone of the Internet.
The diagrams in this article were created using ASCIIFlow. Some content is referenced from Wikipedia.