HomeGlossaryPort 587

What is port 587?

A key part of email marketing strategy is the preparation phase. By ensuring that every aspect of your campaign is set up correctly, you reduce the risk of issues downstream and increase the potential for success. 

Of course, a major part of adequate preparation is planning ahead to minimize deliverability issues while maximizing security. That means it’s necessary to have the correct configurations in place before you begin your send-outs.

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What is an SMTP port? SMTP port functions SMTP port selection Conclusion

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Your SMTP (Simple Mail Transfer Protocol) settings are critical to success, and one of the most important of those settings is your SMTP port selection. Port 587 is one of the possible selections.

What is an SMTP port?

Getting to grips with what an SMTP port is and does requires a fundamental knowledge of how the Simple Mail Transfer Protocol works.

Simple Mail Transfer Protocol, or SMTP, is the standard protocol that is used for sending email messages across networks. 

This protocol is enacted when a user clicks the send button on an outgoing email, at which point their email client connects to an outgoing SMTP server. 

That server then uses the recipient’s email to locate the relevant IP address in the DNS (Domain Name System) and engages in communication with the receiving SMTP server. 

Once this is completed and the email is authenticated, the receiving server delivers the email to the recipient’s mailbox.

A very simplified way of looking at this protocol in action is to break it into three interactions:

  1. Sender to outbound SMTP server.
  2. Outbound SMTP server to inbound SMTP server.
  3.  Inbound SMTP server to recipient.

For this process to function correctly, two critical pieces of information are necessary: The IP address, which identifies the sender device, and the port number, which identifies the service running on that device (i.e. SMTP).

There are several different port numbers, such as ports 25, 2525, and 465. Each of these SMTP ports serve different purposes and are used with varying degrees of frequency. Choosing the correct port is highly important because it can ultimately determine whether or not your email is delivered.

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SMTP port functions

Generally speaking, SMTP ports serve one of two functions: SMTP relay or SMTP submission.

SMTP relay refers to the communication that occurs between two servers when transmitting a message, whereas SMTP submission refers to the process of sending a message to an outbound SMTP server.

For those running their own mail servers, SMTP relay may be a significant consideration. However, for most email marketers, the primary concern is SMTP submission, and your SMTP configuration should reflect this.

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SMTP port selection

In the overwhelming majority of cases, port 587 is the optimal choice for SMTP submission.

Port 25, by contrast, is the default port for relaying mail between SMTP servers, though it is not recommended for submission. This is due to security risks, as spam activity has proliferated on port 25. As a result, attempting to use it for submission will often see your messages fail, as many major ISPs (Internet Service Providers) have decided to block port 25 entirely.

Port 587 is now the standard SMTP port for SMTP submission because it features TLS (Transport Layer Security) encryption. By using port 587, emails sent from your device are more secure and ISPs are far more likely to deliver your messages.

In instances where issues such as blocks occur with port 587, it is possible to use port 2525 as it also benefits from TLS encryption. Failing that, port 465 can be used in rare instances, as some providers do still support it, although it is no longer intended for SMTP communication.

Conclusion

Since SMTP is the protocol that provides the foundation for all the work that you do as an email marketer, it’s paramount that you understand the process and the functions of different SMTP ports.

By and large, the majority of your operations will involve the use of port 587, since it supports TLS encryption and allows for secure SMTP submission.

While other ports, such as port 2525 and port 465, can function as temporary alternatives, port 587 remains the default port for client-to-server communication.

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