Use port 993 with SSL/TLS: the connection is encrypted from the first byte, RFC 8314 recommends it, and 22 of the 23 providers we list use it. Port 143 is IMAP's original port; with STARTTLS it switches to encryption after connecting, and without it everything, your password included, travels in plain text.
Port 993
IMAP over TLS from the first byte. Choose SSL/TLS (sometimes just TLS or SSL) for it. It's what to use whenever your provider offers it.
Port 143
IMAP's original port. With STARTTLS, the app connects in plain text and asks to switch to encryption before signing in. Without STARTTLS nothing is encrypted, so most providers refuse it or don't offer 143 at all. Choosing SSL/TLS on 143, or STARTTLS on 993, fails to connect.
POP3's ports
POP3, the older way to collect mail, uses port 995 with SSL/TLS, or 110, which starts in plain text. Our guides list POP3 for 13 of the 23 providers, all on 995. Which to choose, POP3 or IMAP.
Which port providers use
22 of the 23 providers we list use port 993 with SSL/TLS. The exception is Proton Mail, whose IMAP runs in Proton Mail Bridge on your own Mac, at 127.0.0.1 on port 1143 with STARTTLS. Every provider's servers.
When IMAP won't connect
- The security doesn't match the port: SSL/TLS goes with 993, STARTTLS with 143.
- IMAP is turned off at your provider. GMX, mail.com, Zoho Mail and Xfinity Email each have a setting to turn on first.
- The password is refused. Many providers want an app password in mail apps.
- A network is blocking the port: some VPNs, firewalls and office or school networks block mail ports.
IMAP in LocalInbox
LocalInbox reads every account over IMAP and sends over SMTP; it doesn't use POP3. Each account's Server settings take the port and SSL/TLS, STARTTLS or None. When it can't connect, its message says what went wrong: nothing answering at the port, the wrong kind of security for the port, a certificate this Mac doesn't trust, an unknown server name, or a network that may be blocking the port.
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 port 143 secure?
Only with STARTTLS, which encrypts the connection before you sign in. Without it, your password and mail travel in plain text. Use 993 with SSL/TLS where you can.
What port is IMAP over SSL?
993.
Why does Proton Mail use port 1143?
Proton Mail's servers don't offer IMAP. Proton Mail Bridge, an app on your computer, does, at 127.0.0.1 on port 1143, and passes your mail to Proton encrypted. The Proton Mail guide has the steps: https://localinbox.app/guides/proton-mail