Port 1587 is officially registered with IANA for a service called pra_elmd, operating on both TCP and UDP protocols. The registration lists Dennis Mastin as the contact.1
Beyond that, the trail goes cold.
What We Know (and Don't Know)
Port 1587 sits in the registered ports range (1024-49151)—ports that organizations and developers can request from IANA for specific services. Someone registered this port for "pra_elmd," likely decades ago, but there's almost no public documentation about what the service does, who used it, or whether it's still active anywhere.
The name suggests it might be related to other "elmd" services (Electronic License Manager Daemon or similar licensing systems), but this is speculation. The actual purpose remains unclear.2
Why This Matters
Port 1587 represents something important about how the Internet works: not every port that exists is actively used.
The IANA port registry contains over 47,000 registered ports. Some power the modern Internet—port 443 for HTTPS, port 22 for SSH, port 53 for DNS. Others, like 1587, were registered by developers for projects that never gained widespread adoption, services that became obsolete, or internal systems that never needed public documentation.
These ports still exist in the registry. They're still technically assigned. But they've become archaeological artifacts—evidence that someone, somewhere, built something and needed a port number for it.
Security Considerations
Because port 1587 has no widely-known service running on it:
- You probably shouldn't have anything listening on it unless you specifically configured it
- If you find something listening on port 1587, investigate what it is—it could be legitimate internal software, or it could be malicious software trying to hide in an obscure port
- Obscurity is not security—attackers scan all ports, not just the famous ones
How to Check What's Using Port 1587
On Linux or macOS:
On Windows:
If something is listening, the command will show you which process opened it.
The Registered Ports Range
Port 1587 belongs to the registered ports range (1024-49151). This range is managed by IANA, and ports within it can be registered by organizations for specific services. The registration process provides a way to avoid conflicts—two different services shouldn't use the same port number for different purposes.
But registration doesn't guarantee adoption. Anyone can request a port number for their service. Whether that service becomes widely used, or fades into obscurity like pra_elmd, is another matter entirely.
Related Ports
Other registered ports in the same range:
- Port 1433 - Microsoft SQL Server
- Port 1521 - Oracle Database
- Port 1723 - PPTP VPN
Some become essential infrastructure. Others, like 1587, become footnotes.
Frequently Asked Questions About Port 1587
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