BRev Port 995 — POP3S
Port 995 is POP3 inside TLS, negotiated before any protocol command — the same implicit-TLS design as 465 and 993. It fixes the one fatal flaw of port 110: credentials and message bodies are encrypted in transit, so the network path can no longer read the mailbox. Our reference marks it safe to expose, because that is exactly what it was designed for.
What it does not fix is POP3’s data model. The protocol still downloads messages to one client, still has no server-side folders, and still has no shared read state — so a phone and a laptop configured against the same POP3S account behave like two separate mailboxes. That is a design property of POP3, not something TLS touches.
Where POP3S remains genuinely useful is deliberate archival: pulling messages down to a machine that keeps them, and freeing quota on a small mailbox. For that job it is a perfectly good, encrypted, authenticated protocol. For a normal multi-device mailbox, IMAPS on 993 is the right answer.
One modern complication is authentication rather than encryption. Microsoft 365 and Google Workspace have both retired basic username-and-password authentication for POP and IMAP in favour of OAuth 2.0, so a script or appliance that has fetched mail over 995 for years can stop working on a date set by the provider — with an error that reads like a wrong password. If a legacy device cannot speak OAuth, the remaining options are an app-specific password where the provider still offers one, or a small relay that fetches with OAuth and re-serves locally.
Port 995 at a glance
| Field | Value | Detail |
|---|---|---|
| Port | 995 | Well-known |
| Service | POP3S | POP3 over TLS. (TCP) |
| Category | Mail | sending and collecting email |
| Exposure | Safe | Safe to expose |
Should port 995 face the internet? Encrypted and authenticated — the correct public alternative to 110.
Built to face the internet: authenticated, encrypted, and expected to take unsolicited connections. Still patch it.
What commonly goes wrong
Connection fails while 110 works
Check that the client is set to SSL/TLS rather than STARTTLS for 995 — an implicit-TLS port expects the handshake immediately, and a client that sends POP3 commands first will hang. Certificate name mismatches also surface here, because 110 never validated one; openssl s_client -connect host:995 shows the chain the server presents.
Only some messages download, then it stops
Usually the server enforcing a per-session message limit, or a single oversized message that the client retries forever. Fetch with the UIDL list visible if the client supports it, and check the mailbox in webmail — a stuck message is easy to spot there and impossible to see through POP3.
Check port 995 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 995 — swap example.com for the host you are actually testing.
Is port 995 reachable on another host?
nc -vz example.com 995"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 995 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 995Read TcpTestSucceeded: True = open. It is built in — nothing to install.
telnet example.com 995A 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:995Handy when telnet is not installed: "Connected to …" proves the TCP handshake, without curl trying to speak HTTP.
What on this machine is holding port 995?
sudo ss -tlnp | grep :995Lists the listening socket and the PID/program holding it. Drop sudo and you get the socket but not the process name.
sudo lsof -i :995The macOS answer to "address already in use". Kill it with `kill -9 <PID>` once you are sure what it is.
netstat -ano | findstr :995The 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 | |
|---|---|---|---|---|---|
| 995 | tcp | POP3S | POP3 over TLS.Encrypted and authenticated — the correct public alternative to 110. | Safebrowser-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 995 secure?
Yes — TLS is established before any POP3 command, so credentials and message content are encrypted end to end between client and server. It is the correct replacement for cleartext port 110.
Should I use 995 or 993?
993 (IMAPS) for a normal mailbox used from more than one device, because the server keeps folders and read state. 995 (POP3S) only when you deliberately want mail pulled down to a single machine.
Does 995 use STARTTLS?
No. It is implicit TLS — the handshake happens first. STARTTLS on POP3 runs on port 110 as an upgrade, which is the weaker arrangement because it can be stripped.