IMAP (Internet Message Access Protocol) is the standard way a mail app reads email that stays on your provider's server. The app shows what's there and sends back what you do, so mail you read, move, flag or delete changes on the server, and your phone, your computer and webmail all show the same inbox. It runs on port 993 with SSL/TLS, or 143 with STARTTLS. Sending is a separate protocol, SMTP.
How IMAP works
Your mail app signs in to your provider's IMAP server with your address and a password, often an app password made for that one app. It lists your folders, fetches the messages' headers, and fetches a message's body when you open it. It keeps the connection open, so the server can tell it about new mail as it arrives (IDLE) instead of being asked every few minutes.
Whatever you do in the app is done on the server: a message you read is marked read there, one you move to a folder moves there. That's why another device, or webmail, shows the same thing a moment later.
IMAP and SMTP
IMAP only reads. To send, the app hands the message to your provider's SMTP server, which delivers it; most apps then save a copy to your Sent folder over IMAP. So a mail account has two sets of settings, incoming (IMAP) and outgoing (SMTP), each with its own server, port and security: see IMAP's ports and SMTP's ports.
IMAP or POP3
POP3 is the older way to collect mail: it downloads new messages to one device, and what you do there isn't sent back. IMAP keeps everything on the server and in step. All 23 providers we list offer IMAP, and our guides list POP3 for 13 of them, from their own help pages. POP3 and IMAP compared.
IMAP settings
To add an account by hand, a mail app needs the incoming server's name, its port and its security (SSL/TLS or STARTTLS), your user name (usually your full address) and your password. Your provider's help pages list them.
22 of the 23 providers we list use port 993 with SSL/TLS. Every provider's IMAP and SMTP settings are on one page, with a guide to each.
| Setting | What to enter |
|---|---|
| Incoming server | Your provider's IMAP server, such as imap.gmail.com |
| Port | 993 (or 143) |
| Security | SSL/TLS on 993, STARTTLS on 143 |
| User name | Usually your full email address |
| Password | Your password, or an app password if your provider asks for one |
Versions
Most servers speak IMAP4rev1, published as RFC 3501 in 2003. IMAP4rev2, RFC 9051 from 2021, brings in what servers had added since, IDLE among it. Apps and servers agree on what both support when they connect, so you don't choose a version.
IMAP in LocalInbox
LocalInbox reads every account over IMAP and sends over SMTP; it doesn't use POP3. It keeps the mail it has synced on your Mac, so reading, search and rules work offline; changes you make offline go to the server when you reconnect. LocalInbox fills in the settings for AOL Mail, Fastmail, Gmail, GMX, iCloud Mail, Proton Mail, Yahoo Mail and Zoho Mail; for any other provider, choose Other IMAP account and type them in.
Sources
What this page says about the protocols comes from their standards, checked in November 2026. The providers' numbers are counted from our settings guides, each checked against the provider's own help pages, and what it says about LocalInbox comes from the app.
Questions
Is IMAP secure?
With SSL/TLS or STARTTLS, yes: your password and your mail travel encrypted between the app and the server. Without either, on port 143 alone, they travel in plain text, and most providers no longer allow that. RFC 8314 recommends SSL/TLS from the first byte, on port 993.
Does IMAP download my email?
It fetches copies to show you, and many apps keep them for offline reading and search. The messages themselves stay on the server until you delete them, which is why every device sees them.
Do I have to turn IMAP on?
With some providers, yes. GMX, mail.com, Zoho Mail and Xfinity Email each have a setting to turn on before a mail app can connect; the guides say where: https://localinbox.app/imap-settings
What does IMAP stand for?
Internet Message Access Protocol.