Module 1 · 1.2

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IMAP, POP and webmail: why you see the same email everywhere

Module 1: How your email works · Reading time: 9 minutes

Learning objective: After this lesson you can explain the difference between IMAP and POP, you know what it means for your email on several devices, for your storage and for a backup, and you can check how your devices are set up.

Key concepts: IMAP, POP3, synchronising, flags, Sent folder, storage limit (quota), local copy

Two ways to collect email

In lesson 1.1 you saw that email is delivered to a mail server. It stays there until an email program collects it. There are two protocols for collecting email, each based on a very different idea.

POP3 (Post Office Protocol, POP for short) is the oldest. The idea is a PO box: your program collects the new email, stores it on your computer, and the server may then throw it away. The standard says so itself: normally, email is downloaded and then deleted.
IMAP (Internet Message Access Protocol) works the other way round. The email stays on the server. Your program shows what is on the server and passes on what you do: reading, moving, deleting, flagging. The server is the source, and your devices look along with it.

Webmail always works with IMAP. It can't work any other way: webmail has no disk of its own to store your email on. It shows live what is in your mailbox on the server.

What IMAP synchronises

With IMAP, not only the email itself stays in sync, but also everything you do with it:

Folders. If you create a folder Klanten (Customers) in webmail, it also appears in the email app on your phone. Folders are stored on the server.
Flags. Every message has properties that IMAP calls flags: read, replied, flagged, deleted. If you read an email on your phone, it also shows as read in webmail. If you reply to it on your laptop, you see the replied arrow in webmail.
Moving and deleting. If you drag a message to Trash, it has been moved to Trash everywhere.

One thing that surprises many people: the Sent folder. Sending goes through SMTP, and SMTP stores nothing. After sending, your email program itself puts a copy in the Sent folder on the server. With IMAP, that copy is visible everywhere. If a program doesn't do this, or puts the copy in a different folder, you only see your sent email on that one device. Lesson 5.1 goes into this further.

What POP does, and why that causes problems

With POP, the program asks the server: which messages do you have for me? It collects them and asks the server to delete them. Many programs have an option like "Leave a copy on the server", sometimes with a period such as 14 days. But even then, the server doesn't know what you do on your computer. Folders, read or replied all stay on that one device.

Take Daan, Sanne's colleague. Years ago he set up his email on his office computer with POP. On his phone he uses IMAP. What happens?

In the morning, Daan sees an email from a supplier on his phone. When he opens his email program at the office, it collects the email and deletes it from the server. After that, the email has disappeared from his phone.
In webmail, the Inbox is almost empty, because everything is on the office computer.
What Daan sends from the office is only in Sent on that computer.

This is sometimes described as POP on a second device "stealing" the email. It is one of the most common causes of the complaint "my email keeps disappearing".

Storage: the storage limit applies to everything

With IMAP, all your email is on the server. Every mailbox has a maximum size, the storage limit or quota. This limit applies to all folders together: the Inbox, but also Sent, Drafts, Archive, Spam and Trash. So deleted email in Trash counts until you empty the trash.

When the mailbox is full, no new email can come in. The sender then gets the email back with an error message. With POP this is less of an issue, because the server keeps being emptied. That is the only reason some people still use POP. It is better to work with IMAP and tidy up now and then, or to store old email locally with an email program (lesson 5.4).

The broken laptop

Suppose Sanne's laptop falls off the table and won't start any more. What has she lost?

With IMAP: none of her email. She logs in to webmail or sets up her new laptop, and everything is back: folders, sent email, read and unread. What may be gone: drafts that weren't on the server yet, and email she had moved herself to a local folder on the laptop.
With POP: all email that the laptop collected and the server deleted. If she had no backup of the laptop, that email is gone.

So IMAP is a form of safety, but not a backup. If you delete a message and empty the trash, it is gone everywhere at once. A mistake synchronises just as quickly as a good action. That's why it's good to know whether your provider makes backups, and how to export important email yourself.

Which settings belong to which protocol

In your email program, the account settings show what kind of account it is. Things to look for:

Protocol	Usual port	Used for
IMAP	993 (SSL/TLS)	reading, email stays on the server
POP3	995 (SSL/TLS)	collecting to one device
SMTP	465 (SSL/TLS) or 587 (STARTTLS)	sending

These are the usual encrypted ports, at WebOké too. An account can only ever use one way of collecting email. If you want to switch from POP to IMAP, in most programs you have to add the account again. First make sure the email that is only stored locally is safe, for example by dragging it into the new IMAP folders.

In practice: how it works in webmail

Webmail always uses IMAP. So what you do in webmail shows up in every email program that also works with IMAP, and the other way round. You can see how full your mailbox is in the bottom left of webmail, in the bar below the folders. The Roundcube manual explains under What is webmail how webmail and an email program work together. Other webmail, such as Gmail or Outlook.com, works in a similar way: they also show what is on the server.

Summary

POP collects email to one device and usually deletes it from the server; IMAP leaves the email on the server.
IMAP synchronises folders and flags (read, replied, flagged). Webmail always works with IMAP.
The Sent folder is a copy that your email program puts on the server itself.
The storage limit applies to all folders together, including Trash and Spam.
IMAP protects you against a broken device, but it is not a backup: deleting happens everywhere at once.

Quiz

Exercise

Exercise D1.2: How your email is set up. On every device you use for email (computer, phone, tablet), look in the account settings to see whether it uses IMAP or POP, and which server and port it uses for receiving and sending. Write this down in a list. Then open webmail and the email app on your phone side by side and compare the folders: do you see the same folders, and is the same email in Sent? Then answer these questions: Does one of your devices use POP, and if so, does that make email disappear from your other devices? Where is your Sent folder: on the server (visible everywhere) or only on one device? What would you lose if your most important device broke tomorrow?

Exercise D1.2: How your email is set up

You do this exercise yourself; no one checks it. Tick off what you've done and mark the exercise as done.

I have looked up the account settings on every device where I read email.
I know for each device whether it uses IMAP or POP.
I have compared the folders in the webmail with those on my phone.

Which devices do you use, and which protocol does each one use (IMAP or POP)?

Which server and port for incoming mail do you see?

Do you see the same folders on all devices, including Sent? If not, where is the difference?

Your ticks and notes only stay in this browser; we don't send them anywhere. If you're signed in, we only save in My courses that you've done the exercise.

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