whatportis.com
suggest an edit →

Port 50Remote Mail Checking

The Remote Mail Checking Protocol (RMCP) is an early protocol designed to facilitate remote access to email servers for users to verify mail status without downloading full email content. It enables lightweight communication to determine if new messages are present, providing basic functions similar to what modern POP3 would later formalize. Its use has diminished over time due to advances in email retrieval technologies and secure protocols..

inEmailNetwork Services
transport
tcp · udp

2 transports registered

in transit
cleartext

payload readable on path

assignment
official

registered with iana

risk
4/10

caution

lookups
7,907

rank 643 of 993 · top 65%

Technical Details

what runs on :50

The Remote Mail Checking Protocol (RMCP) was created to allow email clients to remotely query mail servers to check for new messages, primarily focusing on lightweight status queries rather than full mail retrieval. It allowed clients to connect and determine the presence of new or unread mail without transferring large amounts of data, saving bandwidth and reducing server load.

Functionally, RMCP operates over both TCP and UDP port 50, utilizing TCP for reliable connection-based inquiries and UDP for faster, connectionless status checks. The protocol facilitated user mailbox queries by issuing simple commands and receiving succinct responses, reflecting a minimalist approach to mail interaction before more comprehensive standards emerged.

Over time, RMCP became largely obsolete, replaced by protocols like POP3 and IMAP, which provide richer functionality including authentication, mail downloading, folder management, and synchronization. Nonetheless, understanding RMCP offers insights into the evolution of email protocols and early design priorities such as efficiency and low overhead communication.

Security Information

exposure of :50

risk score

4/ 10caution

worth attention. how exposed you are depends on configuration — don't leave it reachable from the internet without a reason.

email averages 3.9 across 42 ports — this one sits 0.1 above.

in transit

cleartext

credentials and payloads are readable by anyone on path

assignment

official

registered with iana for this service — scanners fingerprint it by number

reachable over

tcp · udp

udp is connectionless — source addresses are trivially spoofed and it is a reflection favourite

security overview

Common vulnerabilities associated with RMCP stem from its age and lack of inherent security features. Typical issues include:

  • Lack of encryption, making it vulnerable to eavesdropping and interception.
  • No built-in user authentication, leading to potential unauthorized mail status checking.
  • Susceptibility to spoofing and man-in-the-middle attacks due to unprotected communication.

Mitigations for these vulnerabilities include:

  • Replacing or disabling RMCP in favor of secure, modern protocols like POP3S, IMAPS, or web-based email with TLS encryption.
  • Utilizing network-level protections such as firewalls and access controls to block port 50 traffic externally.
  • Implementing strong authentication gateways and monitoring network traffic to detect unauthorized activity targeting legacy protocols.

Related Ports

all 42 in email →

the 8 most looked-up other ports in email — 42 ports carry that label.

portservicerisk
:143IMAPcaution
:995POP3Scaution
:109POP2caution
:2096cPanel SSL Webmailsafe
:110POP3caution
:993IMAPScaution
:1352Lotus Notes RPCcaution
:24Private Mailcaution

risk mix of the 8 listed

  • safe13%
  • caution88%

3 of 8 encrypted