What is the difference between IMAP and POP email?

This choice is made once, in a setup screen most people click through, and it explains a family of otherwise baffling problems: mail that vanishes from the phone, folders that exist on the laptop only, and years of email lost with a failed hard drive.

Step by step

1. Work out which you are using.Look at the account settings in your mail program. The account type is shown as IMAP or POP. Webmail is always effectively IMAP-like, because everything lives on the server.
2. Understand what IMAP does.Mail stays on the server; devices show a synchronised view. Read on the phone, and it is read on the laptop. Folders, deletions and replies all sync.
3. Understand what POP does.The program downloads messages to that one computer. By default it then deletes them from the server, so the phone never sees them and no other device can.
4. Know POP's one advantage.Mail is stored locally and does not count against server storage, which suited small mailboxes twenty years ago. It also means the only copy is on one machine, which is the same fact stated as a risk.
5. Check the leave-on-server setting if you keep POP.POP accounts can be configured to leave a copy on the server. If you are staying with POP, this is essential, and it lets other devices see mail as well.
6. Back up local mail before changing anything.Years of POP mail exist only on that computer. Export the mailbox to a file, or copy the mail data folder, before touching the account setup.
7. Move to IMAP by adding, not replacing.Add the same account as a new IMAP account alongside the POP one, then drag the old local folders into the new account. They upload to the server and become available everywhere.
8. Verify on a second device before removing the old account.Check the mail is genuinely on the server by looking at webmail from a browser. Only then remove the POP account.

Tips

• Uploading years of mail to a server can take hours and may exceed a free storage tier. Do it in batches, oldest first.
• Even with IMAP, mail on a server is not a backup. Export an archive annually if the correspondence matters.
• If a provider only offers POP, that is a sign the service is very old. It is usually a good moment to move to a modern provider.

Common mistakes

• Removing a POP account to 'start again' with IMAP — Removing the account can delete the local mail store with it. Every message that was only on that computer goes with it.
• Setting up POP on a second device — Two devices both downloading and deleting means mail arrives on whichever collected it first, and neither has the full picture.

If it doesn't work

Questions people ask