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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 .
As with all SMTP extensions, SMTP AUTH is advertised in the EHLO response, along with a list of supported authentication methods. These methods may change after issuing STARTTLS, typically allowing plain text passwords in the latter case only. RFC 4954 provides the following example ("C:" and "S:" are not part of the protocol, they indicate ...
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 ...
Late 1998 this was revoked when STARTTLS was standardized.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.
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 RFC specifies this code should be returned by teapots requested to brew coffee. [18] This HTTP status is used as an Easter egg in some websites, such as Google.com's "I'm a teapot" easter egg. [19] [20] [21] Sometimes, this status code is also used as a response to a blocked request, instead of the more appropriate 403 Forbidden. [22] [23]
Download QR code; Print/export Download as PDF; Printable version; In other projects Appearance. move to sidebar hide. ... List of port numbers. Add languages ...
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.