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Port 57Mail Transfer Protocol

Mail Transfer Protocol (MTP) was an early protocol designed to transfer electronic mail reliably across computer networks. It predated SMTP and provided basic functionalities to send, relay, and receive messages, but due to limitations and evolving requirements, it was largely deprecated in favor of more robust standards like SMTP..

inEmailNetwork Services
transport
tcp

single transport

in transit
cleartext

payload readable on path

assignment
unofficial

used by convention

risk
4/10

caution

lookups
9,434

rank 509 of 993 · top 51%

Technical Details

what runs on :57

Mail Transfer Protocol (MTP), operating over TCP port 57, was among the first protocols developed to facilitate electronic mail transmission between hosts on ARPANET and early internetworks. MTP was designed to offer reliable delivery services by establishing a persistent, connection-oriented communication channel for the transfer of emails.

MTP functioned using a simple command-response exchange to initiate mail sending, verify delivery, and transfer message data. While it supported basic forwarding and relaying, it lacked many advanced features later required for large-scale email infrastructure, such as sophisticated queuing, error reporting, and extended addressing capabilities.

Due to these limitations, along with the expansion of the internet and more complex requirements, MTP was eventually replaced by the Simple Mail Transfer Protocol (SMTP) starting in the early 1980s. SMTP built upon the foundational ideas of MTP, introducing flexible command sets, better interoperability, and increased extensibility, making it the dominant standard for email transfer since then.

Security Information

exposure of :57

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

unofficial

used by convention, not registered — what answers here varies by deployment

reachable over

tcp

every listening transport is another surface to filter at the edge

security overview

Common Vulnerabilities

  • Since MTP was designed in an era with minimal focus on security, it includes no encryption or authentication mechanisms.
  • Lack of access control makes it susceptible to eavesdropping, spoofing, or unauthorized message relaying.
  • Due to its deprecated and unsupported nature, running MTP services may open legacy systems to exploitation through unpatched vulnerabilities.

Common Mitigations

  • Disable and decommission any legacy services relying on MTP in favor of SMTP with proper security measures.
  • Use encrypted protocols such as SMTPS or implement Transport Layer Security (TLS) to protect email communication.
  • Employ strong access controls, firewalls, and network segmentation to isolate and protect critical mail infrastructure from unauthorized access.
  • Regularly audit network services to detect and remove outdated protocols like MTP.

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