Port143— IMAP / STARTTLS
IMAP on TCP 143 can upgrade a connection with STARTTLS when supported. It differs from implicit TLS on port 993.
Registry assignments, software defaults and local listeners are different things. A port number alone does not identify or secure a service.
Configuration and troubleshooting
Match the client port, TLS mode, hostname and authentication settings to the server. Separate TLS negotiation errors from login failures.
Important limitations
Do not send passwords without a trusted encrypted connection. Selecting port 143 alone does not enable STARTTLS.
Read-only checks: run on the server host
Choose the commands for your OS. Check TCP and UDP separately. No result is not a lasting availability guarantee; inspect host and container separately.
Linux
sudo ss -ltnp 'sport = :143'macOS
sudo lsof -nP -iTCP:143 -sTCP:LISTENWindows PowerShell
Get-NetTCPConnection -LocalPort 143 -State ListenSources and review
Sources checked on:
This review covers the explanations and sources on this page, not your device or every community software entry below.
Software Using This Port (4 software)
Community software entries: links are references, not individual verification.
IMAPMail
Internet Message Access Protocol
Usage Suggestions
- Before using port 143, please confirm it is not occupied by other services
- If you encounter port conflicts, consider using other ports or stopping the occupying service
Frequently asked questions
What is port 143 used for?
Port 143 sits in the Email & Messaging category. This page lists the registered purpose and the software commonly associated with it; to see what is actually listening on a specific machine, check the process with ss/netstat.
Is port 143 TCP or UDP?
The registered protocol on this page is TCP. The same number behaves independently on each protocol: TCP may be listening while UDP is idle, so check them separately.
How do I check if port 143 is in use?
On Linux: sudo ss -tlnp 'sport = :143' for an exact port match. On macOS: sudo lsof -nP -iTCP:143 -sTCP:LISTEN. On Windows PowerShell: Get-NetTCPConnection -LocalPort 143 -State Listen. A listener counts as confirmed only when you can see the bind address and process name; without root/admin you will not see other users' processes.
Is port 143 secure? Should I open it in my firewall?
A port number has no inherent security — it depends on whether the listening service is correctly configured and whether it needs exposure at all. Keep loopback/internal-only services firewalled; where public access is required, pair it with source restrictions, VPN or authentication. The caution section on this page lists port-specific risks.
Quick Info
- Port
- 143
- Protocol
- TCP
- Categories
- Email & Messaging
- Usage Status
- 4 software in use
Related Ports
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