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HomeSales and MarketingEmail MarketingWhat is port 2525 and what is its function?

What is port 2525 and what is its function?

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The Simple Mail Transfer Protocol (SMTP) is the standard protocol for transmitting emails from one computer to another. Whenever you type an email and hit send, you first transfer the data from your system to your email server, from which it goes to the recipient’s. SMTP is the set of instructions guiding the data towards its destination.

To distinguish between various types of incoming network data, computers use ports. A port is just a number telling the recipient which application should process the particular data packet. For example, if a packet is identified by port number 80, it will be processed by a program which is currently “listening”, i.e. waiting for incoming traffic on port 80 (as a matter of fact, it’s your web browser). Every network-capable application uses its own ports, and email programs are no exception. 

This article will explain what SMTP port 2525 is, and how it functions. Port 2525 is not among the most commonly acknowledged, or “well-known” ports like 25, 587, or 465. It is an alternative that can be used if the standard SMTP ports are unavailable. However, it’s not officially recognized as a standard SMTP port by the Internet Assigned Numbers Authority (IANA).

SMTP Ports

There are four main SMTP ports at present: 25, 587, 2525, and 465. Let’s dive deeper into them before highlighting the characteristics of 2525.

Port 25

This is the oldest port, established over four decades ago. Those were the days when no one could even think of using email for nefarious purposes. All communications on port 25 were unencrypted and often did not even require authentication. Unfortunately, its popularity caused spammers and malicious actors to abuse this port. 

In the long run, many email providers have opted to block this port entirely. However, it’s still widely used for server-to-server transmission, although it’s less commonly used for client-to-server email submission.


This port was established in the 1990s to allow people to send encrypted messages using the SMTPS protocol (SMTP over SSL). It was deprecated for a time but has seen a resurgence and is now often used for secure SMTP submission using SSL/TLS. 

Port 587

This is the universal default port for submitting emails from email client programs to servers. As per RFC 2476, issued in 1998, port 587 is recommended for email submission. This is your default option if you do not know which port to use and have to determine the proper one by trial and error.


This is an alternative port to 587, supported by many email service providers (ESPs). While 2525 is not recognized as an official port by the IANA (Internet Assigned Numbers Authority) or the IETF (Internet Engineering Task Force), most ESPs support it and allow customers to send messages seamlessly via this unofficial port. It’s used primarily in environments where standard SMTP ports are blocked. 

When Should You Use Port 2525?

2525 is an alternative to try when 587 is not working. 

587 is the default port to submit your email. However, it might be unavailable for various reasons. In that case, you can go with 2525 and still deliver your message seamlessly. 

It’s important to note that the availability of port 2525 depends on the email service provider (ESP), as it’s not a standard port officially recognized by the Internet Assigned Numbers Authority (IANA). Instead of 2525, your ESP could technically choose another port number. The best way to find out how to properly set up your connection will be by checking the provider’s documentation or asking the support team for help.

To summarize, 587 or 2525 are the default ports you can usually count on. 25 and 465 are less common ports that suit specific purposes, so avoid using them if you do not know precisely what you are doing. 

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