HomeGlossaryPort 25

What is port 25?

When you’re preparing an email marketing strategy, it’s important first to lay the groundwork so everything runs smoothly when you start your send-outs. To that end, you’ll want to ensure that you have set up the correct infrastructure that enables you to reliably reach your recipients’ inboxes while maintaining your security.

An important part of these preparations is configuring SMTP settings and selecting the right SMTP port, with multiple options to choose from. Port 25 is one such option.

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What is an SMTP port? SMTP port 25 What are the uses of the different SMTP ports? Which SMTP port should you use? Conclusion

What is an SMTP port?

To properly understand what an SMTP port is, it’s necessary to have a basic grasp of what SMTP is and what it does.

SMTP (Simple Mail Transfer Protocol) is a standard protocol that email clients around the world use to send and receive messages online. When an email user sends a message, their mail client connects to an outbound SMTP server, which then communicates with the DNS (Domain Name System) to access the recipient’s information and route the email to their inbox.

When connecting to an SMTP server, two critical pieces of data are required. The first is the IP address, which identifies a specific device in a network. The second is the port, which identifies an application being used on that device, such as SMTP.

There are various SMTP port options, such as ports 25, 2525, and 587, and each has a different purpose. Selecting the appropriate port for your purposes is important because it can be the deciding factor in whether or not your messages end up being delivered.

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SMTP port 25

Port 25 is often referred to as the original or official SMTP port. It is the oldest of all the SMTP ports, having been originally introduced in 1982, and has long been used as the standard port.

However, due to a relative lack of security, port 25 has been increasingly used by spammers over the years. As a result, the majority of ISPs (Internet Service Providers) block port 25. Nonetheless, port 25 still has a part to play in SMTP.

What are the uses of the different SMTP ports?

As mentioned above, SMTP ports have different use cases, so your choice of SMTP ports depends on what you’re trying to achieve. Generally, when deciding on an appropriate port to use, you should consider whether you need it for relay or submission.

When sending an email, the sender’s client connects to an outbound server that uses information from the DNS to communicate with an inbound server responsible for the receipt of the message. The term “relay” refers to the process of transmitting that message from one server to the next.

Submission, on the other hand, refers to the process of submitting a message to an outbound SMTP server. This is a client-server interaction in which the user’s mail client communicates with a server.

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Which SMTP port should you use?

While port 25 plays an important role in the relay aspect, it is not the recommended option for sending outgoing mail. The truth is that unless you are running a mail server, you are unlikely to have a real use for SMTP port 25.

As an email marketer, your primary concern should be submission, which means you require a highly secure port for your operations.

When configuring a site or mail with which to send outgoing mail, you will most likely want to choose port 587 instead. SMTP port 587 is the new standard port for sending mail as it ensures secure sending with TLS (Transport Layer Security) encryption, protecting your data and ensuring that your messages are accepted by ISPs.

Conclusion

SMTP configuration is a key part of the preparation phase when enacting an email marketing strategy, so it’s important to understand the process of SMTP and the roles that various ports have in email exchange.

Port 25 is the original SMTP port, and while it still serves an important function in SMTP relay, the relatively insecure nature of this port means that it has fallen out of favor for SMTP submission. As such, using port 25 to send outbound mail can be detrimental to deliverability.

All told, while SMTP port 25 is perfectly usable for server-to-server interactions, the majority of your email marketing needs will necessitate the use of the more secure and reliable port 587.

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