Port 57
Mail 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..
Technical Details
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.