ilona titova/Getty Images IMAP (short for Internet Message Access Protocol) is an internet protocol that lets you sync your email inbox across multiple devices. Most popular email apps, like Gmail and Outlook, use IMAP servers to keep your email the same on every device. If your email uses a POP server instead, it'll only work well with a single computer. When you set up your email on a new phone or app, you need to pick what email client you use (Gmail, Yahoo, etc.). And if you don't pick a specific client, you have to specify whether you're using an IMAP or POP email.