465 and 587 are two SMTP ports that play a major role in delivering emails from one address to another. A common question is a difference between these two ports; this article will answer just that.

What Is SMTP?

This abbreviation stands for Simple Mail Transfer Protocol, the most popular protocol for sending and receiving emails over the web. A port is a communication endpoint that facilitates the transfer of data using a given protocol. With ports, it is possible to tell which parts of the traffic between computers should be processed by a particular application. When setting up your email client software, you’ll be prompted to select a port number, among other SMTP settings.

Web Services and Ports

Two main governing bodies oversee the implementation of web services and ports:
  • The first is the Internet Assigned Number Authority (IANA) which oversees IP address allocation and the domain name management system. This agency also maintains several service protocols and SMTP ports, which is the focus of this article. Anyone can register a new service if a port is unclaimed.
  • The second is the Internet Engineering Task Force (IETF), which creates standards to maintain the Internet's usability. This agency publishes RFCs (Request for Comments) that propose updates to improve the internet.
The primary concern of this article is the RFCs for the SMTP protocol using ports 465 and 487.

TLS and StartTLS

Another set of technical terms you should be familiar with to understand Ports 465 and 587 is TLS and StartTLS. These two terms are related to keeping the contents of an email secure.

  • TLS is a security protocol that enables end-to-end email data encryption. It uses digital keys to encrypt an email message as it's transmitted from the sender and decrypt it once it lands in the recipient's inbox. This prevents hackers or malicious actors from snooping on private and sensitive information.
  • StartTLS is not a security protocol by itself. Instead, it is a command informing the email server that the user wants to switch from an insecure connection to a secure one.

Difference between Ports 465 and 587

The main technical difference between Ports 465 and 587 is that the former uses the TLS security protocol, while the latter use StartTLS.

Port 465: TLS

Port 465 started in 1997 when a group of computer scientists published a proposal for a new encryption standard for SMTP messages. After the submission, port 465 was registered with the Internet Assigned Number Authority (IANA).

But, because 465 was not formally submitted as an RFC with the Internet Engineering Task Force (IETF), it wasn’t formally recognized as an SMTP encryption port. At some point, it was even removed from the IANA registry, but protests caused the IETF to officially recognize the port and reinstate the registry.

After serving as an encryption port for some time, the IANA reassigned 465 for a different use and deprecated it. Despite the reassignment, many email service providers still support 465 for sending SMTP emails.

Port 587: StartTLS

587 was formally recognized as an SMTP encryption protocol in 1997, the same year that 465 was registered. Since its inception, 587 has remained the default for encrypted communications using the Simple Mail Transfer Protocol.

Which Is the Best Port to Use?

587 is the best port to use because it is officially recognized for email encryption. If 587 is unavailable or not working as expected, then you can go with 465.

In summary, don’t use 465 unless there’s no other option. 587 is the best one to use.


Many technicalities are involved in sending emails from one address to another, and ports are one of them. We’ve explained two essential ports, their distinct features, and when you should pick one over the other.

Ensure that the email service provider you choose supports these SMTP ports and other options you may need to avoid problems with delivering your messages. UniOne is an example of such a provider, and it enables you to send bulk transactional messages with ease.