IMAP vs POP3: which should you use for your email?

Three protocols, three jobs

When you set up a mail app it asks about two servers, and that split explains most of the confusion. Sending and reading mail are separate jobs, handled by separate protocols:

So the real choice is only between IMAP and POP3, and only for reading. Whichever you pick, your app still sends through SMTP. The settings for each are covered in IMAP and SMTP settings for mail apps.

How POP3 works

POP3 (Post Office Protocol version 3, RFC 1939) was designed in an era of dial-up connections and one computer per person. The model is a post office box: the app connects, downloads whatever is waiting, and disconnects. By default the messages are then deleted from the server; most apps offer a "leave a copy on the server" option, often with a "remove after N days" setting.

That model has consequences that are easy to miss:

• Only the inbox. POP3 has no folders. Whatever you sort into folders exists only on the device that did the sorting.
• No shared state. Read, replied and flagged marks stay on the device. A second device that also uses POP3 sees every message as new, or misses the ones the first device already deleted from the server.
• Sent mail stays local. Messages you send are stored in the Sent folder of the device you sent them from. Your phone never sees what you sent from your laptop.
• The device is the archive. If the laptop dies and there is no backup, the mail is gone - the server deleted its copy long ago.

How IMAP works

IMAP (Internet Message Access Protocol - version 4rev1 in RFC 3501, updated as IMAP4rev2 in RFC 9051) treats the server as the home of your mailbox. Apps connect to it and work on the server's copy: they list folders, fetch messages, and set flags such as \Seen (read), \Answered and \Flagged. Every app connected to the same mailbox sees the same result.

• Folders live on the server, including Sent, Drafts and Trash, so every device has the same structure.
• State is shared. Read a message on your phone and it is read on your laptop; delete it on the laptop and it disappears from the phone.
• Download only what you need. An app can fetch headers first and the body or a large attachment only when you open it - useful on a phone with a slow connection.
• New mail can be pushed. With the IDLE extension (RFC 2177) the app keeps a connection open and the server tells it about new mail immediately, instead of the app checking every few minutes.

Side by side

Offline access is not a reason to choose POP3

A common belief is that you need POP3 to read mail without a connection. Modern IMAP apps cache messages locally and work offline too: Thunderbird, Outlook and Apple Mail keep a local copy you can search and read on a plane, and queue changes (moves, deletions, read marks) until you are back online. On phones, how much is cached depends on the app's sync settings - set it to keep more days of mail if you rely on offline reading.

Why providers recommend IMAP

Almost every mail provider steers users to IMAP, and the reason is simply how people use mail now: a phone, a laptop, maybe a tablet and webmail, all expected to show the same mailbox. IMAP was built for that; POP3 can only approximate it with "leave a copy on the server", and even then folders, read status and sent mail don't follow you between devices.

Security is not the difference. Both protocols are equally safe when the connection is encrypted with TLS (port 993 for IMAP, 995 for POP3) and equally unsafe without it. What differs is where your mail ends up: with IMAP the provider's server holds it; with POP3 your device does, which makes the device - and its backups - your responsibility.

When POP3 still makes sense

• You read mail on exactly one computer and want the messages stored there, under your own backup regime.
• Your provider's storage is very small and you deliberately empty the server.
• An old device or a piece of software only speaks POP3 - a scanner, a ticketing tool or a script that collects mail from a mailbox.

For everyone else IMAP is the better default. If you are worried about the server being the only copy, make your own: a desktop IMAP app with offline storage enabled is a simple, automatic local backup.

IMAP on AnyMail (and no POP3)

AnyMail supports IMAP only; there is no POP3 server. That is a deliberate choice: an AnyMail inbox is shown in the web app, in mail apps and, for shared inboxes, to several people at once, and all of them have to agree on what has been read, sent or deleted. POP3 can't express that. Apps connect to anymail.tech on port 993 with SSL/TLS, using an app password created for the inbox - see the mail app setup guide for each client.

• Inbox, Sent, Drafts, Trash and Junk are always there, and you can add your own folders (and folders inside folders) from the mail app or the web app - both see the same ones. Deleting a folder moves its mail to Trash rather than erasing it.
• Reading and deleting in a mail app shows up in the web app and vice versa. Deleting from the Inbox moves a message to Trash, as it does in the browser.
• IMAP IDLE is supported, so apps that use it are told about new mail straight away.
• The account's data export includes every message and attachment, so the server is never the only place you can get your mail from.

Moving from POP3 to IMAP

Switching an existing setup over takes a few minutes, but do it in this order so nothing goes missing:

1. Leave the old POP3 account in place for now and add the same address again as a new IMAP account. Most apps can't convert an account from POP3 to IMAP in its settings.
2. Check that the IMAP account shows the messages still on the server. Anything POP3 already downloaded and deleted will only be in the old account's local folders.
3. Copy the old local mail into the IMAP account's folders by dragging it across. The app uploads it to the server, and from then on every device sees it. With AnyMail you can upload into Inbox, Sent and your own folders this way; imported messages keep their sender, subject, date, body and attachments, though not every original header.
4. When everything is there, remove the POP3 account from that device, and set up IMAP on your other devices.