Port 465 (SMTPS)
Port 465 is mail submission over implicit TLS (IANA name submissions): your email app connects, starts TLS immediately and then sends your outgoing mail through your provider.
- Service
- SMTPS
- Protocol
- TCPTCP. IANA also lists UDP 465, but for a different, unrelated service (IGMP over UDP); mail never uses UDP.
- IANA registry
- Officially assigned: submissions (Message Submission 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 465?
Encryption starts before any data is sent, which is why RFC 8314 now prefers 465 for submission. On a mail server, require authentication on 465; an open submission port is a spam relay.
Sources
“Port 465 is already in use”: how to fix it
The error means another program is already listening on port 465. 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 :465taskkill /PID <PID> /FmacOS
lsof -nP -iTCP:465 -sTCP:LISTENkill <PID>Linux
sudo ss -ltnp | grep :465sudo lsof -i :465sudo kill <PID>Replace <PID> with the number from the last column (Windows) or the PID column (macOS, Linux).
Port 465 vs 587
Both are for sending mail from an app to your provider. 465 encrypts from the first byte (implicit TLS); 587 starts in clear text and upgrades with STARTTLS. RFC 8314 prefers 465, but 587 is just as widely supported: use whichever your provider lists, and never send without TLS.
Port 587 (SMTP submission)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 465 used for?
Port 465 is mail submission over implicit TLS (IANA name submissions): your email app connects, starts TLS immediately and then sends your outgoing mail through your provider.
Is port 465 TCP or UDP?
TCP. IANA also lists UDP 465, but for a different, unrelated service (IGMP over UDP); mail never uses UDP.
Is it safe to open port 465?
Encryption starts before any data is sent, which is why RFC 8314 now prefers 465 for submission. On a mail server, require authentication on 465; an open submission port is a spam relay.
How do I free port 465 if it is already in use?
Find the process: on Windows run netstat -ano | findstr :465 and stop it with taskkill /PID <pid> /F; on macOS or Linux run lsof -i :465 and stop it with kill <pid>.