BRev Port 465 — SMTPS / implicit-TLS submission
On port 465 the TLS handshake happens before any SMTP is spoken — implicit TLS, the same model as HTTPS. There is no plaintext phase to attack, which is its whole advantage over 587’s STARTTLS upgrade: a network attacker cannot strip an advertisement that was never sent in the clear.
Its history is why people are unsure about it. 465 was assigned for SMTPS in the 1990s, then deprecated in favour of STARTTLS on 587, then reassigned to another protocol entirely, and finally restored for mail submission by RFC 8314 in 2018 under the name “submissions”. That means guidance written between about 1998 and 2018 tells you not to use it, and current guidance recommends it. The current guidance is right.
Marked care in our reference for the same reason as 587: it is legitimately public — roaming users have to reach it — but only with authentication. TLS on the wire says nothing about who is allowed to send; an authenticated submission service is the requirement, and TLS is how the credentials survive the trip.
Port 465 at a glance
| Field | Value | Detail |
|---|---|---|
| Port | 465 | Well-known |
| Service | SMTPS / submissions | Mail submission wrapped in TLS from the first byte. (TCP) |
| Category | Mail | sending and collecting email |
| Exposure | Care | Expose with care |
Should port 465 face the internet? Correct for clients sending mail — with authentication, always.
Legitimately public in some setups, but only hardened — current version, real authentication, rate limits, and ideally an allow-list.
What commonly goes wrong
The client hangs or reports a protocol error on 465
Nearly always a STARTTLS setting on an implicit-TLS port: the client sends SMTP in the clear while the server waits for a TLS ClientHello, and both sit there. Set the connection security to “SSL/TLS” rather than “STARTTLS” for 465. openssl s_client -connect host:465 should complete a handshake immediately and then show the SMTP banner.
Old documentation says port 465 is deprecated
It was, between the late 1990s and 2018, and a great deal of the internet still repeats it. RFC 8314 restored it as the preferred submission port precisely because implicit TLS cannot be downgraded. If your provider offers it, it is a current, correct choice.
Check port 465 yourself
No browser can open a raw TCP socket, so no web page can honestly tell you whether this port is open on a remote host. These are the real commands, generated for port 465 — swap example.com for the host you are actually testing.
Is port 465 reachable on another host?
nc -vz example.com 465"succeeded!" means the TCP handshake completed — the port is open. "Connection refused" is closed; a hang until timeout means filtered (a firewall dropped it silently).
nmap -Pn -p 465 example.comThe only common tool that distinguishes open / closed / filtered. -Pn skips the ping sweep, so it still works against hosts that ignore ICMP.
Test-NetConnection example.com -Port 465Read TcpTestSucceeded: True = open. It is built in — nothing to install.
telnet example.com 465A blank screen or a banner means it connected. "Connection refused" means closed. Quit with Ctrl-] then `quit`.
curl -v --max-time 5 telnet://example.com:465Handy when telnet is not installed: "Connected to …" proves the TCP handshake, without curl trying to speak HTTP.
What on this machine is holding port 465?
sudo ss -tlnp | grep :465Lists the listening socket and the PID/program holding it. Drop sudo and you get the socket but not the process name.
sudo lsof -i :465The macOS answer to "address already in use". Kill it with `kill -9 <PID>` once you are sure what it is.
netstat -ano | findstr :465The last column is the PID. Match it in Task Manager’s Details tab, or `taskkill /PID <pid> /F`.
No web page can tell you whether a port is open on a remote host
A browser cannot open a raw TCP socket — there is no API for it, by design. So a site that reports “port 3389 is OPEN on 203.0.113.10” is not checking from your browser; it is asking its own server to scan on your behalf. That works, but it means their server sees the host you asked about, scans from their address rather than yours, and answers a question about their network path, not yours.
We don't have a server here and won't pretend to. So this page does three honest things instead:
| Port | Proto | Service | What it is | Exposure | |
|---|---|---|---|---|---|
| 465 | tcp | SMTPS / submissions | Mail submission wrapped in TLS from the first byte.Correct for clients sending mail — with authentication, always. | Carebrowser-blocked |
http://host:port/ and times it. A connection that is established proves a socket is open; an instant refusal usually means nothing is listening; anything else is honestly reported as “can't tell”. Each attempt gives up after 2.5s.nc -vz example.com 443
nmap -Pn -p 443 example.com
telnet example.com 443
curl -v --max-time 5 telnet://example.com:443
This page cannot answer that, and neither can any other page — from your browser. Opening a TCP connection to an arbitrary host and port is not something JavaScript is allowed to do. Every “open port checker” that gives you a green tick is running the scan on their server. Which is fine, as long as you know what you are agreeing to: they learn which host and port you were worried about, and the answer they give you is about the route from their data centre — not from the internet as your users see it.
What to do instead
Run the check from outside your own network. Copy an nmap or nc line from the card above and run it from a machine that is not behind the same router — a phone on mobile data with a terminal app, a cheap VPS, a colleague's laptop. Running it from inside the LAN tests the LAN, not the internet, and will happily say “open” while the world sees nothing.
Then check the thing that is actually blocking it, in this order: the service is bound to0.0.0.0 and not 127.0.0.1 · the host firewall (ufw, firewalld, Windows Defender Firewall) · the cloud security group or the router's port-forward rule · and finally your ISP, which commonly blocks 25, 80 and 445 on residential lines whatever you configure.
What a browser genuinely can verify
One thing: that an HTTPS service answers. If what you actually want to know is “is my site up and how fast is it”, the latency test measures real round trips to a CORS-open URL. If the name doesn't resolve, or resolves somewhere unexpected, that is a DNS problem, not a port problem — and it is the more common cause of “my port is closed” than an actual firewall.
An IP address finds the machine; a port picks which program on it gets the traffic. TCP sets up a connection first — a handshake, ordered delivery, retransmission — which is why the web, email and SSH use it. UDP just sends the packet with no handshake and no guarantee it arrives, which is why DNS, video calls and games use it: late data is worse than lost data.
That difference is why a UDP port is so much harder to test. TCP either completes a handshake or it doesn't, so a tool can tell you. A UDP service that has nothing to say to an unexpected packet stays silent — and silence looks identical to a firewall dropping it.
The three ranges
0–1023Assigned by IANA to core services. On Unix, binding one needs root (or CAP_NET_BIND_SERVICE).1024–49151Registered by vendors for their applications. Any user can bind these — which is why every dev server lives here.49152–65535Never assigned. The OS hands these out as the SOURCE port of your outgoing connections. (Linux actually uses 32768–60999 by default.)Closed is not the same as filtered
Closed means the host answered: the packet arrived, nothing is listening, and you got an immediate refusal (a TCP RST). Filtered means nothing answered at all — a firewall dropped your packet in silence, so you wait for a timeout and learn nothing. The difference matters: closed proves the host is reachable and the port is free; filtered tells you only that something between you and it is discarding traffic.nmap reports the two separately. A browser cannot distinguish them, which is why this page reports a timeout as “can't tell” rather than guessing.
The one habit worth keeping
Bind services to 127.0.0.1 instead of 0.0.0.0 unless something outside the machine genuinely needs them, and reach them over SSH or a VPN. Every database on the never-expose list above ships with that advice, and the leaks all begin the same way: a default bind address, a cloud instance with a public IP, and a scanner that found it within the hour.
The blocked-port list this page uses is the WHATWG Fetch Standard's “bad port” table — the ports every browser refuses to connect to (Chrome calls it ERR_UNSAFE_PORT). Local probing is additionally gated by Chrome's Local Network Access permission, which replaced Private Network Access and ships in Chrome 142.
FAQ
Is port 465 deprecated?
No — that guidance is out of date. RFC 8314 (2018) re-registered 465 for message submission over implicit TLS and recommends it alongside 587. Documentation predating that still calls it deprecated.
What is the difference between 465 and 587?
465 negotiates TLS before any SMTP command, so there is never a cleartext phase. 587 starts in the clear and upgrades via STARTTLS, which an active attacker can attempt to strip if the client does not require encryption. Both are authenticated submission ports.
Can I use 465 for server-to-server delivery?
No. Inter-server transfer is port 25, and receiving servers do not look for 465. 465 is for authenticated clients submitting mail to their own provider.