Port 993 (IMAPS)
Port 993 is IMAP over implicit TLS: the encrypted way for mail apps to read messages kept on the server. Gmail, Outlook.com and most providers expect 993 for IMAP.
- Service
- IMAPS
- Protocol
- TCP
- IANA registry
- Officially assigned: imaps (IMAP over TLS protocol), TCP
Check if a port is open on your IP
We only check the address you are visiting from, one TCP port at a time. You cannot enter someone else’s address: this is not a port scanner.
Is it safe to open port 993?
Traffic is encrypted from the first byte, so 993 is the recommended IMAP port. On a server, the remaining risk is password guessing: enforce strong passwords or app passwords and rate limiting.
Sources
“Port 993 is already in use”: how to fix it
The error means another program is already listening on port 993. Find its process ID (PID), then stop that program or start yours on a different port.
Windows (Command Prompt or PowerShell as administrator)
netstat -ano | findstr :993taskkill /PID <PID> /FmacOS
lsof -nP -iTCP:993 -sTCP:LISTENkill <PID>Linux
sudo ss -ltnp | grep :993sudo lsof -i :993sudo kill <PID>Replace <PID> with the number from the last column (Windows) or the PID column (macOS, Linux).
Port 993 vs 995
Both are encrypted mail retrieval. 993 is IMAP: messages stay on the server and sync across devices. 995 is POP3: messages are downloaded to one device. For a phone plus a laptop, choose IMAP on 993.
Port 995 (POP3S)Why a port can look closed when your server is running
Most home networks sit behind a router doing NAT: the router owns the public address, and your computer has a private one such as 192.168.1.10. A connection from the internet reaches the router and stops there unless you add a port forwarding rule to your computer.
Many mobile and some home providers go further and use carrier-grade NAT (CGNAT): several customers share one public address, and your router itself gets an address from 100.64.0.0/10. Then no rule on your side can open a port; ask the provider for a public IP or use a tunnel or VPN service.
Even with forwarding in place, the firewall on the computer (Windows Defender Firewall, ufw, firewalld) must allow the port, and the program must listen on all interfaces (0.0.0.0), not only on 127.0.0.1.
UDP cannot be checked this way: a UDP service usually stays silent to packets it does not understand, so “no answer” means nothing. This check uses TCP only.
Frequently asked questions
What is port 993 used for?
Port 993 is IMAP over implicit TLS: the encrypted way for mail apps to read messages kept on the server. Gmail, Outlook.com and most providers expect 993 for IMAP.
Is port 993 TCP or UDP?
Port 993 uses TCP. IANA registers it for TCP.
Is it safe to open port 993?
Traffic is encrypted from the first byte, so 993 is the recommended IMAP port. On a server, the remaining risk is password guessing: enforce strong passwords or app passwords and rate limiting.
How do I free port 993 if it is already in use?
Find the process: on Windows run netstat -ano | findstr :993 and stop it with taskkill /PID <pid> /F; on macOS or Linux run lsof -i :993 and stop it with kill <pid>.