POP Treats the Mailbox Like a Delivery Point
POP, short for Post Office Protocol, was built around a simple model: a mail app connects to the mail server, collects new messages, and stores them on the device. The server is a handoff point, not necessarily a permanent home for the mail. When “leave a copy on server” is disabled, the app can tell the server to remove each message after downloading it.
That can make one computer the practical home of an account’s inbox. The messages remain in that app’s local storage, but a phone or second computer may find nothing to download later. If the first device is lost or its mail files are damaged, the server may no longer have those messages either.
One Setting Changes What Other Devices Can See
The distinction matters because POP and IMAP handle mail differently. IMAP is designed to keep messages on the server and synchronize what devices see—such as read status and folders. POP generally retrieves messages, with the server-copy option determining whether they remain available for another device to fetch.
Keeping server copies can help when several devices need access, but it also means mail remains stored on the provider’s servers and may count toward storage limits. Removing them can reduce that server-side accumulation, but it is not a backup strategy: the only remaining copy may be on one device. Before changing the setting, check where the app stores downloaded mail and whether that local data is backed up. A tiny checkbox can decide whether an old message is waiting in the cloud—or only on the computer that first collected it.
