eli5: How exactly are emails sent, like the actual process of the data getting sent to another device that’s for example on another continent?
In: Technology
There are a bunch of standard communications protocols that make up what we call “The internet,” like **H**yper**t**ext **T**ransfer **P**rotocol (http) which transfers webpages from their server to your device.
When you send an email, your computer converts the text and the relevant formatting information into a message, which it transmits to the recipient’s mail server using a protocol called Simple Mail Transfer Protocol (SMTP.) When a user “checks their email,” they download messages from the mail server using one of two protocols – Internet Message Access Protocol (IMAP) or Post Office Protocol Version 3 (POP3.)
Essentially the process is – you compose an email, SMTP sends it to the recipient’s mail server. Recipient downloads the email from the server using IMAP or POP3.
Hi 🙂
How Eli5 would you like it? 😉
– E-Mails aren’t getting sent from your outbox to someone’s inbox,
– but rather over your internet provider’s connection
– to your email service,
– over their internet through different connections across the globe,
– to the recipient’s server…
– Where it waits to be downloaded (Either until they check or sending out a “Hey, you have new mail” to their client).
Let’s say your mailbox is mysupergreatmailbox444 at Hotmail.com.
and you send a message to Germany, e.g. ilovetogetmailsfromoverseas222 at GMX.de.
– You write the E-Mail and hit send.
– If you use an email client, there will be settings like server, port, account password, and so on.
– Internet & Computers doesn’t work with names like “Hotmail” or “GMX”, but with IP addresses (numbers like 123.222.127.333 or a more modern format).
– Your computer asks your internet provider or other “DNS” (Domain name service, basically a phone book) what IP address (a number) Hotmail.com has.
– Then your e-Mail client will connect to that server’s number with your log-in data, trying to establish a connection.
(If you write an email on your email provider’s site, that step basically gets skipped. You instead log in to the website and save the email there directly.)
– Hotmail then saves your mail to your account’s outbox, sends it to the receiver. If it fails it will retry a couple of times.
– Similar process. Hotmail asks a DNS what IP-Address GMX.de has. Then tries to send the data over the internet tubes to that server’s IP.
– Each transfer is made up from different little pieces of information, and gets collected at the other end. So your eMail might get send in little chunks across different routes, servers, across sub sea cables, ground lines, satellite. Imagine you write a 10 page letter and send each page through a random postal service. The recipient sorts them if they arrive out of order. If a page goes missing, the recipient will ask for it again. It’s rather chaotic 🙂
– The recipient’s mail client will check their provider’s (GMX in the example) server—
– You’ve guessed it. The E-Mail client will look up GMX’s IP address, connect with log-in data. Send and download messages.
– The recipient’s E-Mail program uses either a protocol like IMAP (TL;DR: Synchronizes new messages with the server and your other devices) or the older POP3 protocol (Basically downloads and deletes).
– The E-Mail client will download & display the message. If they use their E-Mail provider’s website, they will display the mails as website to look at and thus provide a human interface to the saved E-Mails.
Never have the recipient’s E-Mail program and yours interacted directly. Not unlike regular mail.
Internet communications are generally governed by the Open Systems Interconnection (OSI) Model. The OSI model works as a set of different protocols that get layered on top of each other, adding additional information as you go up the layers.
Layer 1 is the Physical layer. This is the (until the creation of wi-fi) actual wire that’s connecting two devices, where data is sent as ones and zeros at a certain rate of speed, with certain error correcting mechanisms.
Layer 2 is the Datalink layer. This covers communication between a group of devices on the same physical network, and includes ways for each device to uniquely identify itself, and to send information to one specific device, or broadcast to everyone on a network. If you’ve ever heard of MAC addresses, this is the layer that those come into play
Layer 3 is the Network layer. This is the heavy lifting layer that really forms the Internet, and is here the ideas of routing traffic between networks and TCP/IP addresses get involved.
Layers 4-7 we’ll just gloss over for now as they don’t come into play much for our purposes.
Emails are generally sent over an Internet protocol called Simple Mail Transfer Protocol, or one of its more secure descendants. This handles connections to a mail server for sending email out, and connections between mail servers for delivery.
Now comes the metaphor. Think of your computer/mail client program as your house, and the local post office as the mail server. You mail out a letter by going to the post office with a message, you put a return address on it and a delivery address on it. and the post office takes it. That’s what SMTP does for you. It talks to the server, inputs a destination e-mail address, a “from” e-mail address and a message.
Now the post office works to deliver your letter. Based on the destination ZIP code, it knows to get the letter to the post office for that particular zip code. It then gets fed into the whole shipping and logistics operation of the mail to get to that destination. Similarly, the mail server looks at the domain for the destination e-mail (the part after the @), and uses another protocol called Domain Name Service (DNS) to look up what TCP/IP address the mail server for that domain is. Then it uses TCP/IP to transfer the message across the internet to the destination mail server wherever that may be.
When the destination post office gets the letter, it stores it in your PO box (to keep the metaphor, it doesn’t deliver the mail). The email server similarly keeps the message in under your username.
When you go to the post office to check your PO Box, you use your key, then check to see if there are any letters in your mailbox, take them out, and bring them home to open them.
In the digital world, your email client program connects to the server, gives its username and password (key) checks the number of new messages in the mailbox and downloads them.
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