Before executing your email marketing strategy, it’s necessary to lay the infrastructural foundation to ensure everything goes smoothly. One of the particular things to do is select the appropriate SMTP ports to ensure your emails get to the intended recipients.
The oldest SMTP port, 25, was adopted in 1982 as the default port. Since then, SMTP port delegation has undergone many changes alongside the broader SMTP ecosystem. This article will summarize what you need to know about SMTP ports.
What Is an SMTP Port?
Let’s start by explaining what SMTP is. It’s an abbreviation for Simple Mail Transfer Protocol (SMTP), the set of rules for sending emails from one server to another.
When you write an email and click the send button, you’re instructing the email contents to be transferred from your mail server to that of the recipient. SMTP is the protocol guiding the data transfer and ensuring it gets to the correct recipient.
A port is an endpoint that information reaches as it’s transferred from one server to another. Think of it as the virtual person on the receiving computer who sorts and delivers the incoming data packets from your SMTP server to the recipient’s one.
SMTP Port Uses
The SMTP protocol has two main use cases: mail relay and mail submission.
Submission is the process of transferring a message from an email client to its assigned email server. When you type a mail and click the send button, mail submission is the first step that occurs.
Relay involves transferring email contents from one email server to another. It’s how the email goes from your SMTP server to that of the intended recipient.
Port 25
25 is the original and oldest SMTP port introduced in 1982. Originally SMTP was designed to send unencrypted emails. It was quite fit for the task, but its lack of security posed a future problem.
Over time, spammers began abusing this endpoint to send unwanted, often harmful messages. Malicious actors seemingly roamed free on this port, causing many internet service providers (ISPs) and email service providers (ESPs) to take action. Later many ISPs and ESPs blocked it altogether. These days, 25 is still used for email relaying but not for submission.
It’s not advisable to use 25 to send emails because you’ll likely run into errors. Using 25 means your message may fail to get to the intended recipient.
What Other Ports Are Available?
We’ve mentioned that you should avoid using 25 because many ISPs and ESPs don’t accept traffic on this port. Fortunately, there are other ports you can use.
465
This endpoint was established in 1997 to allow people to send emails securely with the Secure Sockets Layer (SSL) protocol. This data transfer protocol allowed users to send encrypted emails. Many businesses flocked to 465 thereafter.
However, the IANA (Internet Assigned Numbers Authority) and IETF (Internet Engineering Task Force) reassigned 465 for different uses barely a year after its creation. This reassignment meant that many people who switched to 465 were left with a deprecated endpoint.
This endpoint still exists but has been deprecated, making it inadvisable to use it to send emails.
587
587 was established by the IANA and IETF in 1998. It was designed for secure mail submission with the Transport Layer Security (TLS) protocol, which superseded the SSL. 587 is the default SMTP port for mail submission and should be used as the primary option.
2525
2525 is an alternative secure endpoint for when 587 isn’t working. It has the same capabilities for secure email submission, but the nitpick is that it is not yet officially recognized as an SMTP port. Nonetheless, most ISPs and ESPs support 2525, and you can use it to send emails successfully.
