How an email gets from one inbox to another

Email is like the post, but faster

Email works much like the postal service. You write a message and address it. You hand it to your local post office, which works out where it needs to go and passes it to the post office at the other end. That office holds it in a mailbox until the recipient collects it.

In email, the post offices are mail servers: computers run by your email provider that send, receive and store messages. See What is a server?

The journey, step by step

1. You press Send. Your mail app, or the email website, passes the message to your provider's outgoing mail server.
2. Finding the destination. The server looks at the part of the address after the @, for example example.com. It uses the internet's phone book, DNS, to ask: "which server handles mail for this name?"
3. Delivery. Your server connects to that mail server and hands the message over, using an agreed set of rules for sending mail. Most providers now encrypt this hop.
4. Checks at the door. The receiving server looks for spam, viruses and signs that the sender is faking who they are.
5. Storage. If it passes, the message is placed in the recipient's mailbox on that server.
6. Collection. The recipient's app connects and fetches it, and their phone may show a notification.

All of this usually takes seconds. If the receiving server is busy or offline, your server keeps the message and tries again later, sometimes for a day or more.

Why your emails appear on every device

Most mail apps today keep the messages on the server and sync them to your devices. Read an email on your phone, and it shows as read on your laptop too. Delete it in one place, and it disappears everywhere. This is usually done with a method called IMAP.

An older method, POP, downloads messages to one device and may remove them from the server. If you have ever found emails on an old computer that never appeared on your phone, that is probably why. Most people are better off with the syncing kind.

Bounces and spam folders

If an email cannot be delivered, you usually get a bounce message back. Common reasons are a typo in the address, a full mailbox at the other end, or an attachment that is too large.

Mail that arrives but looks suspicious goes to the spam or junk folder. Providers decide this from many signals, including whether the sending server is allowed to send for that address. Organisations set up behind-the-scenes records, with names like SPF, DKIM and DMARC, that let receiving servers check a message really came from them. If you are expecting an email that has not arrived, always check your spam folder.

Spotting a fake

Here is the important part for your safety: the name shown next to a message is just a label the sender chose. Anyone can make an email appear to come from "Your Bank" or "Royal Mail". Checks catch many fakes, but not all, and criminals also use addresses that look almost right.

• Tap or hover on the sender's name to see the full email address. Look closely at the part after the @.
• Be suspicious of urgency: "your account will be closed today", "a parcel is waiting, pay a small fee".
• Do not click links to log in. Open the app or type the company's address yourself.
• If a friend or colleague sends an odd request for money or gift cards, check with them another way, such as a phone call.

Tip: Your email account is the key to your other accounts, because password resets are sent there. Give it a strong, unique password and turn on two-step verification. The password checker can help you see how strong yours is.

Want the technical version? See Phishing basics and Application protocols.