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Email is submitted by a mail client (mail user agent, MUA) to a mail server (mail submission agent, MSA) using SMTP on TCP port 587. Most mailbox providers still allow submission on traditional port 25. The MSA delivers the mail to its mail transfer agent (MTA). Often, these two agents are instances of the same software launched with different ...
The port numbers in the range from 0 to 1023 (0 to 2 10 − 1) are the well-known ports or system ports. [3] They are used by system processes that provide widely used types of network services. On Unix-like operating systems, a process must execute with superuser privileges to be able to bind a network socket to an IP address using one of the ...
Only servers listening on port 587, or private servers, should be configured that way, not a Message eXchange (MX). However, the historical trait that SMTP is not authenticated by default results in a different behavior with regard to access protocols, in some cases; for example, when using AUTH EXTERNAL after STARTTLS. [9]
Late 1998 this was revoked when STARTTLS was standardized. [2] With STARTTLS, the same port can be used with or without TLS. The use of well-known ports for mail exchanges communicating with SMTP was discussed in particular at the time. [3] Port 465 currently shows [4] as registered for both Source-Specific Multicast [5] and submissions.
Several protocols use a command named "STARTTLS" for this purpose. It is a form of opportunistic encryption and is primarily intended as a countermeasure to passive monitoring . The STARTTLS command for IMAP and POP3 is defined in RFC 2595 , for SMTP in RFC 3207 , for XMPP in RFC 6120 and for NNTP in RFC 4642 .
One more benefit is that with a dedicated port number, 587, it is always possible for users to connect to their domain to submit new mail. To combat spam (including spam being sent unwittingly by a victim of a botnet ) many ISPs and institutional networks restrict the ability to connect to remote MTAs on port 25.
Other ports on the Corps of Engineers list include the Port of Houston in the number one spot. South Louisiana is second, then Corpus Christi; New York/New Jersey; Long Beach, California; New Orleans; Beaumont and Baton Rouge. As of May 2024 the Port of Lake Charles surged to the number 10 on the list below. [2]
STARTTLS for IMAP, POP3 and ACAP: RFC 2606 : Reserved Top Level DNS Names: June 1999: Fictitious domain name: example.com, .test, ... RFC 2740 : OSPF for IPv6: December 1999: OSPF: RFC 2743 : Generic Security Service Application Program Interface Version 2, Update 1: January 2000: GSSAPI v 2: RFC 2744 : Generic Security Service API Version 2 ...