Port 218 is officially assigned to MPP (Message Posting Protocol)—a protocol documented in RFC 1204 in February 19911. It runs on both TCP and UDP. You won't find it running anywhere today, but it solved a real problem in its time.
What MPP Did
Personal computers in the early 1990s had no operating system mechanism for user authentication. You turned on the computer and you were... someone. This was fine for spreadsheets but terrible for email, where proving sender identity matters2.
MPP was designed to let PCs post messages to a mail service host with proper authentication. It borrowed the command-reply structure from SMTP (RFC 821) and FTP (RFC 959), creating a way for machines that couldn't authenticate themselves to still send authenticated mail through a central host that could2.
Why It Disappeared
The protocol was marked "Experimental" from the start. As operating systems evolved to include user authentication, network security improved, and email clients became more sophisticated, the specific problem MPP solved vanished. Modern systems authenticate at multiple layers—operating system login, email client passwords, encrypted connections. The gap MPP was built to fill closed.
Well-Known but Unused
Port 218 sits in the well-known ports range (0-1023)—the space reserved for standard Internet services assigned by IANA3. These ports require elevated privileges to bind to on Unix-like systems. Port 218 has a legitimate reservation here, but that reservation points to nothing.
The official IANA registry still lists "mpp" for port 218, with a contact name that dates back to when the protocol mattered4. It's a historical marker more than an active service.
Security Note
Some security scanning tools flag port 218 as having been used by malware in the past5. This is common for assigned-but-unused ports—they're attractive to attackers precisely because legitimate services aren't expected there. If you see traffic on port 218 today, it's worth investigating. It's almost certainly not MPP.
Checking Port 218
On Linux or macOS:
On Windows:
If something is listening, it's not the Message Posting Protocol.
Why This Port Matters
Port 218 is a historical marker. It shows how protocols are born to solve specific problems, live as long as those problems exist, and become obsolete when the world changes. The IANA registry preserves these assignments because port numbers never truly die—they just stop carrying traffic.
The well-known port space is littered with these ghosts: protocols that solved real problems for five years and then stopped mattering. Port 218 reminds us that the Internet we use today was built by people solving immediate, practical problems. MPP was one solution. Better solutions replaced it. The port number remains.
Related Ports
- Port 25: SMTP—the mail protocol that survived and still carries most of the world's email
- Port 587: Message Submission—the modern authenticated email submission port
- Port 110: POP3—another email retrieval protocol from the same era that's mostly been replaced
Frequently Asked Questions
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