Email’s first and most recognizable syntax, the @ symbol, was chosen because it was devoid of meaning. It, prior to email, never appeared in user names or host domains, and wasn’t recognized as an escape character by ARPANET computers of the time. Its uselessness made it useful. And now it’s everywhere.

You can reasonably assume that any app with collaborative features today uses the @ symbol to tag other users. At some point, we even started using ‘at’ as a verb to describe the action. Note-taking platforms use the symbol to link to other pages. Project management software uses it to reference teams and tasks. All of that, and somehow, the @ symbol is arguably the most mundane example of how email changed the knobs and levers of the internet!

For email, more than any other software, has been the place where new software features were incubated before becoming a new default.

Everything behind the curtain

The teletype printers and even telegraphs that preceded email could send one-to-one or one-to-many messages, first broadcasting dots and dashes, then letters and numbers. But only to devices and operators that were on and listening. Email solved that with store-and-forward messaging, letting users log into a server to check their inbox.

Ray Tomlinson, the programmer who added the @ symbol to email addresses, told the Verge that, before email, “There was no really good way to leave messages for people. The telephone worked up to a point, but someone had to be there to receive the call.” Voicemail came after email, if you can believe it. “So everyone latched onto the idea that you could leave messages on the computer.” And, by 1977, people had already begun working on ways to reply to messages in a way that referenced the original.

Threads, as hacker lingo would eventually dub it, first made their way to Usenet. Followed later by Slashdot, Reddit, Facebook, Twitter, and, obviously, well, Threads. Email’s legacy has reached the point where new apps are named after its features!

All of that to say nothing of email’s most significant structural update: content types and the message attachments. Nathaniel Borenstein, one of the inventors of attachments, hates what we call them. He wanted the ability to insert media into messages in-line, not attached separately (he also wasn’t overly concerned with getting email to recognize foreign languages). But separate attachments and multilingual emails is his MIME protocol enabled. Now, a few hundred variations of paperclip icons and plus sign buttons later, another one of email’s progeny is everywhere you look.

Referencing users with an @ symbol, threading conversations, attaching files to messages, these are all structural and technical frameworks. They were dreamt up by email’s earliest hackers, adopted by developers and founders who tried and failed to kill email. 

Not all of email’s legacy came from standards setters and policy wonks, though. 

Tech’s oldest and favorite sandbox

Email’s open standards make it ripe for experimentation. Anyone can build on top of the infrastructure, adding inbox management, message composition, and integration features, while remaining compliant with the sending and receiving protocols like MIME and SMTP. 

Out-of-office replies are, from the perspective of a mail transfer agent and the recipient’s inbox, indistinguishable from normal emails. They are simple client-side automations that, after their release in enterprise email software during the mid-80s, evolved into away messages in AOL Instant Messenger, statuses in Slack, and iPhone’s DND auto-replies. Other than a comically ineffectual RFC pleading for better autoresponder etiquette, the entire movement was driven by vendor innovation.

There were innovations other than those from corporate email, thankfully. Free webmail, fueled by some of the internet’s earliest advertising revenues, put tools like Gmail’s Labels in front of millions of people. Before, in the Megabyte Era of email, you had to move messages from folder to folder, never occupying more than one at a time. Labels, or what you’d more likely call tags today, let you assign as many non-hierarchical, overlapping identifiers as you wanted. Exactly the same as what you’d now do with tasks in Todoist, subscribers in your newsletter, blog posts in WordPress, files in macOS Finder, or whatever you want to categorize and store indefinitely.

“Google believes people should be able to hold onto their mail forever,” the April Fool’s announcement read. Suddenly, the cognitive overhead of triaging your inbox was a fraction of what it used to be. Because you didn’t have to worry about how many free megabytes you had left and whether an email deserved to claim any of them, forever. Most apps followed, making archives the default way to remove items from view without losing them forever, like closing out a Trello card or removing a GitHub repo from active lists. They, like email, usually aren’t stored on-device, so why not make them out of view but always a search away?

Mobile devices almost deserve their own subcategory of email innovations. BlackBerry built a brand new infrastructure that would push emails to your phone in near-real-time, leading Apple to eventually build a standard for push notifications that didn’t just work for email but for any app that wanted to send notifications to your smartphone. 

By reducing friction to push messages to mobile devices, another innovation sprang up to deal with the flood: Mailbox’s swipe gestures. "Our biggest a-ha moment was when we realized that the primary use case of email on the phone is triage," Gentry Underwood explained to the Verge in 2013. With that tiny interface change, archiving and labeling OOO messages, family threads, and order confirmations felt fast and fluid. Which is exactly why it’s the standard for replying to a message in Signal, adding or removing tracks in Spotify, and finding true love on Tinder!

It’s not just communication software and productivity platforms, email has had an outsized impact on how we date and cook and entertain ourselves. Email is one of the best places to grow a community—while some of email’s best features have come from the community that sprung up around it. 

The one thing email hasn’t passed on

Markdown was a standardization of the crowd-sourced effort to add rich-text formatting to text editors that lacked the functionality. And yet it continues to thrive despite every textbox you can imagine including Bold, Italic, and Underline buttons. The ubiquitous share button was originally a “Share this article via email” on blogs and news websites. These were individual innovations and movements. And they happened in email because it provides more control and autonomy than virtually any channel that has followed it.

Every app wants to have the best UX, the smoothest way to add attachments, tag users, categorize content, but few of them want you to leave the walled garden they built. The more portability and optionality you have, the less they make. 

Email, on the other hand, cannot be co-opted. You can always take your list somewhere else, sending from whichever platform offers the latest and greatest. And that’s why it will continue outlasting the competition. It’s why every app that tries to kill email ends up sending it instead.

So, if you want to see software and hardware evolve in real-time, watch your inbox.