SMTP was designated to use port 25 in IETF Request For Comments (RFC) 821. IANA still ...
465. 2525. Port 25 is commonly used for SMTP relay, but you should not use it for SMTP submission because most providers block it. If you want to configure your WordPress site or email client to use SMTP, you should start with port 587 as your first choice, as it’s the standard port for SMTP submission.
SMTP port 25 continues to be used primarily for SMTP relaying. SMTP relaying is the transmission of email from email server to email server. In most cases, modern SMTP email clients (Microsoft Outlook, Mail, Thunderbird, etc.) shouldn't use this port.
SMTP Port 25 uses the TCP as a transmission protocol. Also, Port 25 is the most known and ...
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Port 25: The original standard SMTP port. Port 25 is the original standard SMTP port. Today, the Internet Assigned Numbers Authority (IANA), the group responsible for maintaining the internet addressing scheme, still recognizes port 25 as the standard, default SMTP port. SMTP was designated to use port 25 in IETF Request For Comments (RFC) 821.
The SMTP transmission channel is a TCP connection established between the sender process port U and the receiver process port L. This connection is used as the transmission channel. This protocol is assigned the port 25, which is L=25 as the default transmission channel for communication between mail servers.
To this day, SMTP port 25 continues to be recognized as the default SMTP port for sending email, including by the Internet Assigned Numbers Authority. But that doesn’t mean you should use it. While it’s still technically the default, almost all modern email clients (including Gmail, Yahoo, and others) no longer use it.
By sending a specially-crafted request to TCP port 25, a remote attacker could overflow a buffer and execute arbitrary code on the system or cause the application to crash. References: [ CVE-2011-4040 ], [ XFDB-71086 ], [ BID-50452] SG. 25. udp.