Internet TCP port 25 is primarily used by the Simple Mail Transfer Protocol (SMTP) for the routing of email across the Internet. Software such as Microsoft Exchange Server and Postfix, which are email servers, commonly use this port to send and receive mail messages. Mail clients like Outlook and Thunderbird also use port 25 for SMTP communication. However, due to the prevalence of spam sent over this port, many ISPs and cloud providers block it and use other ports for mail submission.
TCP port 25 is commonly used for Simple Mail Transfer Protocol (SMTP) for sending emails. In the past, hackers have exploited this port to send spam emails or phishing attacks. They have also used it to spread malware or viruses through email attachments. Additionally, hackers have been known to exploit this port to perform a denial of service (DoS) attack, overwhelming the server with traffic and causing it to become unavailable. In some cases, hackers have even used port 25 to gain unauthorized access to systems and steal sensitive data. This has led many ISPs to block port 25 to prevent such exploits.
