Simple Mail Transfer Protocol, or SMTP, is the protocol used for sending electronic mail across networks worldwide. As such, it plays a major role in email marketing, so it pays to have a comprehension of SMTP and SMTP relays.
Moreover, it is good to have some knowledge of the different SMTP ports in widespread use, as well as those which have at one time been considered the standard. Port 465 falls into the latter category.
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| Want to jump ahead? SMTP, ports, and functions Background on port 465 Port 465 vs Port 587 Conclusion |
SMTP, ports, and functions
To understand the role of port 465, it is necessary to outline SMTP ports in general.
Though SMTP is a complex protocol, it can be broken down into three steps.
Step 1: A user writes an email message on their machine, adds the recipient address, and clicks send. Subsequently, the mail client connects to an outgoing mail server responsible for handling sent mail. This client-to-server communication is called SMTP submission.
Step 2: The sender’s SMTP server uses the recipient’s email IP address to access information from the DNS (Domain Name System) and connect with the recipient’s inbound SMTP server. This server-to-server communication is called SMTP relay.
Step 3: The recipient’s inbound SMTP mail server accepts the email and delivers it to their inbox once it has been authenticated.
The SMTP process requires an IP address and a port number to function, and different ports are used for different types of communication.
Port 25 is commonly used for SMTP relay between servers. On the other hand, Port 587 is used for SMTP submission, though port 465 used to fulfill this function.
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Background on port 465
Port 465 was at one time the default SMTP port. This port was initially assigned by the Internet Assigned Numbers Authority (IANA) for a type of encrypted SMTP communication known as SMTPS (Simple Mail Transfer Protocol Secure).
However, port 465 did not retain this status for very long, and is no longer considered the standard for SMTP, with port 587 now being the preferred option.
Because port 465 was the standard for a time, it may still be supported on some legacy systems, but many SMTP servers will actually block connections from port 465.
Port 465 vs Port 587
The primary difference between ports 465 and 587 is how encryption is implemented.
Port 465 uses implicit Transport Layer Security (TLS) encryption. The TLS protocol means that it is necessary to validate trusted certificates at setup in order to establish a connection with a server, and that it is not possible to transmit information in plain text.
Port 587, on the other hand, uses STARTTLS. This refers to a command by which the email client can negotiate the status of the connection with a server, initiating the TLS protocol to create a secure connection.
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Conclusion
Port 465 is a port that was historically used to handle outgoing mail in communication from client to server. At one time, port 465 was the default SMTP port for submission, and was assigned this function by the IANA. However, port 465 has since been deprecated, meaning that it is no longer the recommended option for SMTP submission.
Due to its use of TLS encryption, port 465 remains a more secure option than some other ports that support SMTP submission, such as port 25. With this in mind, it can, in some instances, be used as an alternative SMTP port for submission when experiencing problems. However, fewer and fewer systems support the use of port 465.
Port 465 has been superseded by SMTP port 587. Port 587 is considered the most robust and secure option and, for this reason, it has become the go-to port when it comes to SMTP submission. In the vast majority of cases, it is advisable to use port 587 to handle your outgoing mail and to reserve port 465 for use only when necessary.
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