People across the globe exchange billions of emails each day. This massive information flow is made possible by the Simple Mail Transfer Protocol (SMTP), which facilitates sending emails from one server to another.
Whenever you type an email and hit send, you’re instructing your assigned mail server to transfer the message contents to the recipient’s mail server. SMTP is the protocol guiding this data transfer and ensuring the email gets delivered to the recipient.
To be processed by the right application, every SMTP data packet is tagged with a specific number, called a TCP port number. Port numbers allow the operating system to forward the incoming chunk of data to a specific application processing this type of data.
This article will describe the TCP ports used by SMTP-capable software and their unique characteristics.
What Is an SMTP Port?
A port serves as an endpoint information transfer from one computer to another. Think of it as the virtual bridge that data passes through as it’s transferred from one SMTP server to another, in this case, from mail server A to mail server B.
Every network-enabled computer is identified by a unique string of figures called the IP address. It’s how servers identify themselves to transfer information over the Internet. A port number is another story: it tells the receiving computer which program will process the incoming data. For instance, a particular program may be responsible for handling all data packets tagged with port number 25. An alternative way to put it is that the program is “listening on port 25”.
To sum it up, an IP address identifies a specific computer, while a port identifies a specific type of application on that computer.
SMTP Ports
The SMTP server software uses four primary ports: 25, 587, 465, and 2525. It’s essential to choose the right one when setting up your email client, otherwise you might run into problems.
25
This is the oldest among the four, established in 1982. It was adopted when SMTP was only able to send unencrypted, plain text messages. Unfortunately, many spammers and malicious actors abused this endpoint to send harmful messages, causing email service providers (ESPs) to stop supporting it en masse.
Nowadays many email providers simply block all incoming traffic on this port.
465
This port was established in 1997 to allow people to send emails securely with the Secure Sockets Layer (SSL) transport protocol used to protect the SMTP traffic. However, SSL was later deprecated in favor of TLS (Transport Layer Security). In turn, the 465 port was deprecated in favor of 587, which works with the TLS protocol.
It’s not advisable to use port 465 to submit emails because many ESPs don’t support it.
587
This is SMTP’s default port for sending emails. It was adopted in 1998 and initially destined for secure email submission. If you are setting up your email client and do not know which port to specify, try this value first.
2525
This is an alternative port for secure email submission. But there’s a catch: it’s not one of the officially recognized ports. Despite its informality, many ESPs allow you to send messages via 2525.
You should try using port 2525 if 587 isn’t working for whatever reason.
From the above information, you can conclude that 587 and 2525 are the two primary ports for sending emails. Sending a message with one of these ports means they’ll likely get to the intended recipient.
Ports 25 and 465 are almost never used these days, the former because many ESPs no longer support it and the latter because it has been deprecated in favor of an alternative.
Choosing An SMTP Service
You might pick the right port, but choosing an unreliable SMTP provider means your email may not reach the intended recipient. It’s critical to choose a reliable provider that sends your messages seamlessly.
Consider the following when looking for an SMTP service:
- Security: You need a service with advanced security features to prevent unauthorized data access.
- Reliability: Look for a provider with near-perfect server uptime.
- Customer Support: You should be able to access external help whenever you need it.
- Ease of Use: You need a platform whose interface you can easily navigate.
