Port 143 — 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
Quick Info
- Port
- 143
- Protocol
- TCP
- Categories
- Email & Messaging
- Usage Status
- 4 software in use
Related Ports
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