The POP Setting That Silently Deletes Your Mail
This is one of the more genuinely disruptive, and genuinely avoidable, mistakes I run into. Someone sets up a new device using POP instead of IMAP, and within a day their phone, their old computer, and webmail all stop showing new messages — because POP was, by original design, built to move mail off the server entirely, not keep it synced across everything.
If you haven't already, our IMAP vs. POP3 explainer covers the broader distinction — this piece is specifically about the one setting inside POP that determines whether this actually happens to you.
Why POP behaves this way by default
POP (Post Office Protocol) dates back to an era before most people had more than one device — the assumption baked into its design was that you'd download your mail once, to one computer, and that computer would be the permanent home for it afterward. Downloading and removing from the server made sense in that world. It causes real problems the moment you use more than one device on the same account.
The setting that fixes it
Every POP setup screen includes an option along the lines of "Leave a copy of messages on the server," sometimes with an additional choice for how long to leave them (a set number of days, or indefinitely). If you're setting up any device on POP and there's any chance you'll ever check that account anywhere else — another computer, your phone, webmail — this needs to be turned on.
If mail has already gone missing because of this
- Check the device that was set up on POP first — the mail likely downloaded there and is genuinely present locally, even though it's no longer visible anywhere else.
- If you can access that device, export or back up the mail from there before changing anything else.
- Going forward, switch that device to IMAP instead of POP, or at minimum enable "leave a copy on server" if POP is required for some reason.
The simplest fix, honestly
Unless you have a specific reason to use POP — a legacy system that only supports it, for instance — just use IMAP everywhere instead. IMAP was designed from the ground up for exactly the multi-device situation almost everyone is actually in today, and it avoids this entire category of problem by keeping everything synced rather than moved.