Port 143: IMAP
TCP 143 is the port for Internet Message Access Protocol. Prefer 993 only.
| Service | Internet Message Access Protocol |
|---|---|
| Protocol | TCP |
| Exposure risk | Medium: expose with care |
| Secure alternative | IMAPS (port 993) |
| Range | Well-known (0–1023): binding needs root/admin on Unix |
What port 143 does
Mail clients read and organise mail that stays on the server with IMAP, so several devices see the same folders. Plain 143 can upgrade with STARTTLS.
Should port 143 be open?
Prefer 993 only. Where you can, use IMAPS (port 993) instead.
Find what's listening on port 143
- Linux:
sudo ss -tulpn | grep :143 - macOS:
sudo lsof -nP -i :143 - Windows:
netstat -ano | findstr :143, then look up the PID in Task Manager.
Open or block it in a firewall
- ufw:
sudo ufw allow 143/tcp(ordeny) - firewalld:
sudo firewall-cmd --add-port=143/tcp --permanent && sudo firewall-cmd --reload - Windows:
New-NetFirewallRule -DisplayName "Port 143" -Direction Inbound -Protocol TCP -LocalPort 143 -Action Allow
Port assignment per the IANA Service Name and Transport Protocol Port Number Registry. Test several ports at once with the port scanner, or any port with the open port checker.
Questions about port 143
What is port 143 used for?
Internet Message Access Protocol. Mail clients read and organise mail that stays on the server with IMAP, so several devices see the same folders. Plain 143 can upgrade with STARTTLS.
Is port 143 TCP or UDP?
TCP. IMAP uses TCP port 143.
Is it safe to open port 143?
Medium: expose with care. Prefer 993 only. Secure alternative: IMAPS (port 993).
How do I check if port 143 is open?
Use the checker on this page: it connects to your host on TCP 143 from the internet. Locally, run
nc -vz host 143 (macOS/Linux) or Test-NetConnection host -Port 143 (PowerShell). To see what is listening on your own machine, run ss -tulpn | grep :143 (Linux) or netstat -ano | findstr :143 (Windows).