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

Module 1: How your mail 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 mail 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 mail

In lesson 1.1 you saw that mail is delivered to a mail server. It stays there until a mail program collects it. There are two protocols for collecting it, 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 mail, puts it on your computer and the server may then throw it away. The standard says so itself: normally mail is downloaded and then deleted.
IMAP (Internet Message Access Protocol) works the other way round. The mail stays on the server. Your program shows what is on the server and passes on your actions: reading, moving, deleting, flagging. The server is the source, and your devices look on.

Webmail always works with IMAP. It can't do anything else: webmail has no disk of its own to store your mail on. It shows live what is in your mailbox on the server.

What IMAP synchronises

With IMAP, it's not just the mail itself that stays in step, but everything you do with it:

Folders. If you create a Customers folder in webmail, it also appears in the mail app on your phone. Folders live on the server.
Flags. Every message has properties that IMAP calls flags: read, answered, 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 via SMTP, and SMTP stores nothing. After sending, your mail 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 mail 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 such as "Keep 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 answered stay on that one device.

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

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

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

Storage: the storage limit covers everything

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

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

The broken laptop

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

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

So IMAP is a form of safety, but not a backup. If you delete a message and empty the trash, it's 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 mail yourself.

Which settings belong to which protocol

In your mail program's account settings you can see what kind of account it is. Things to look for:

Protocol	Usual port	Used for
IMAP	993 (SSL/TLS)	reading, mail 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 have one way of collecting mail. If you want to switch from POP to IMAP, in most programs you have to add the account again. First make sure the mail 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 mail program that also uses IMAP, and the other way round. You can see how full your mailbox is from the bar under the folders at the bottom left of webmail. The Roundcube manual explains under What is webmail how webmail and a mail program work together. Other webmail, such as Gmail or Outlook.com, works in a similar way: it also shows what is on the server.

Summary

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

Quiz

Exercise

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

Exercise D1.2: How your mail 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 mail.
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 device 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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