Port 25 is an SMTP port used for SMTP transmissions. It is the primary message transmission channel that helps mitigate attacks from third parties. Many email clients use port 25 to communicate with the outgoing mail server. When sending emails, once you click the send button, the server will connect with the SMTP server via port 25 and provide the information needed for sending the email, such as the recipient address and the email message.
The SMTP server receives this information and handles the delivery of the email message, routing it to the receiving mail server using the necessary network protocols and technologies.
Port 25 is the oldest and first official SMTP port established, and it plays a crucial role in message relaying. Still, port 25 is vulnerable to spam and malware attacks because it supports open relays, so today, many ISPs have blocked it, and ports 465 and 587 are considered more secure and modern than port 25.
What is the Difference Between Ports 25, 465, and 587?
Port 25
Port 25 is the standard and default SMTP port used to communicate between sending and receiving servers during email delivery. Although many email providers and ISPs have started blocking port 25 connections for security reasons, it is still used for SMTP message ports to transfer email from one server to another. However, sending emails using this port is not advisable unless you manage your own mail server.
Port 456
This port was also an email transmission port used for SMTP connections; it was more secure because it offered encryption of email contents. However, many services were left stranded because SMTPs were deprecated after they underwent reassignment by IANA and IETF for different functions.
Some email servers may still be using port 456 to support older email clients that implemented SMTPs, but if you don’t need to maintain a specific legacy, you should not use port 465 to send your emails.
Port 587
Port 587 is just like port 25, both dedicated to SMTP. The difference is that port 587 uses authentication, encryption, and temper-proofing through digital signatures, while port 25 transmits messages in plain text without these capabilities. This is why port 587 is the best port to use when transmitting an email message through an email client.