Why is Port 25 for email transmission no longer widely supported?
Why is Port 25 for email transmission no longer widely supported?Email is used for important communications, and ISPs want to ensure that these communications remains as secure and private as possible. Most ISPs no longer support port 25 for the transmission of email by their residential Internet customers.
Much of the current use of port 25 is conducted by computers that have been infected by malware and are sending spam without the knowledge of the users of those computers. Requiring the use of SMTP authentication helps to prevent infected computers and other devices connected to the Internet from being able to freely transmit spam and malware.
It has been a long standing recommendation from M3AAWG, a highly regarded international working group of anti-abuse professionals, and the Internet Engineering Task Force (IETF), that port 25 be blocked.
We encourage any company that runs a mail server to follow suit and allow only authenticated SMTP traffic.