Port 2525: SMTP alt (convention)
Port 2525 is an unofficial fallback for SMTP mail submission, offered by some providers when a network blocks 25, 465 and 587. It has no standing: IANA registers TCP 2525 to an unrelated service called MS V-Worlds.
| Port number | 2525 |
|---|---|
| Service | Unofficial alternate SMTP submission |
| Protocol | TCP |
| Category | |
| Default encryption | No |
| IANA service name | ms-v-worlds |
| IANA transports | TCP, UDP |
| Used in practice | TCP |
Should you use port 2525 for SMTP?
Only as a fallback, and only if your provider documents it. Because it is not standardised, whether it works and whether it requires TLS depend entirely on that provider's configuration, so you cannot infer anything about it the way you can with 465 or 587.
The reason it exists is filtering. Port 25 is blocked outbound by most consumer ISPs and many cloud providers to contain spam, and some restrictive networks block 587 and 465 as well. A provider offering 2525 gives users on those networks a route out.
If you have a choice, use 465 for implicit TLS or 587 for STARTTLS. If you must use 2525, verify explicitly that the connection is encrypted rather than assuming it, because there is no convention telling you which mode the port runs in.
Which ports are related to port 2525?
The port a reader usually needs next is the encrypted or plaintext twin of this one, so those are listed first rather than buried in a generic list.
What commonly listens on port 2525?
- Transactional mail providers offering it as a documented alternative port
- Self-hosted Postfix or Exim configured with an extra submission listener
How do I check whether port 2525 is open?
Port 2525 carries TCP, so a connection either completes its handshake or it does not, which makes the check definitive.
| Question | Command | What to know |
|---|---|---|
| Is it open on a remote host? | nc -vz example.com 2525 | A TCP handshake either completes or it does not, so netcat gives a definitive answer in one line. |
| Same check on Windows | Test-NetConnection example.com -Port 2525 | Built into PowerShell. TcpTestSucceeded in the output is the answer; telnet is not installed by default on modern Windows. |
| What is listening locally? | ss -tlnp | grep ':2525 ' | Lists the process bound to port 2525 on Linux. On macOS use lsof -nP -iTCP:2525 -sTCP:LISTEN, on Windows netstat -ano | findstr :2525 |
Replace example.com with the host you are testing. A blocked port and a port with nothing listening on it look identical from the outside, so if a service should be running, check locally before blaming the firewall.
Frequently asked questions
Is port 2525 an official SMTP port?
No. The official submission ports are 587 for STARTTLS and 465 for implicit TLS. IANA registers TCP 2525 to MS V-Worlds, which has nothing to do with mail, so port 2525 is purely a provider convention offered when the standard ports are blocked.
Is port 2525 encrypted?
That depends entirely on the provider, because nothing standardises it. Some run STARTTLS on it, some accept plaintext. Check the provider's documentation and confirm the connection negotiates TLS before sending credentials over it.
What is port 2525 used for?
Port 2525 is an unofficial fallback for SMTP mail submission, offered by some providers when a network blocks 25, 465 and 587. It has no standing: IANA registers TCP 2525 to an unrelated service called MS V-Worlds.
Is port 2525 TCP or UDP?
IANA assigns port 2525 on TCP, UDP. In practice it carries TCP. Nothing in any standard mentions port 2525 for mail. It is a provider convention chosen because it is memorable and rarely filtered, and it should be treated as a workaround rather than a configuration to prefer.
Is port 2525 secure?
Port 2525 is not encrypted by default. Where possible, use an encrypted alternative or tunnel it over TLS or a VPN.
Should I open port 2525 on my firewall?
Only if you specifically need SMTP alt (convention). Expose it to the smallest set of trusted sources, and never open database or Windows-service ports to the whole internet.