Billions of emails are exchanged daily, thanks to the adoption of the Simple Mail Transfer Protocol (SMTP) back in the 1980s. This protocol facilitates the seamless transfer of data between email servers. It uses communication endpoints called ports to send messages from one email server to another.
A port is actually just a number that allows a computer to determine the target application that will process the incoming portion of data. More poetic types, however, may think of them as a real-life shipping dock. When you want to send an item to another country, it passes through the shipping dock, where it’s sorted and placed on the ship heading to your intended destination. Computer ports work this way; they’re the virtual endpoints your data passes through before getting to the final recipients.
This article will explain how different SMTP ports work and which ones you should use.
What Is SMTP?
The acronym stands for Simple Mail Transfer Protocol, the standard protocol for sending emails. Whenever you type an email and hit the send button, you transfer the data from your computer to your mail server, and then in turn to the recipient’s one. SMTP is the set of rules enabling this data to reach the right destination. SMTP ports provide a way to follow certain conventions while doing the transfer.
How Does SMTP Work?
Here’s what takes place after typing and sending your email:
- Your email client connects to its assigned server using the SMTP Protocol.
- Your client submits the sender’s and recipient’s email addresses and the message contents to the server.
- The email client checks if the recipient’s and sender’s addresses share the same domain. If so, it immediately forwards the message to the recipient’s mailbox. If not, it consults the domain name system (DNS) for the IP address of the recipient’s mail server and sends the message there, again, using the SMTP protocol.
- The recipient’s server verifies the incoming message and stores it in the recipient’s mailbox.
The above mentioned process typically occurs within seconds of hitting the send button.
The protocol uses four primary ports: 25, 587, 465, and 2525. When setting up your email client, you’ll need to enter the correct value.
This port is the oldest, established in 1982 by the Internet Assigned Numbers Authority (IANA). Since then, it has been the default one for email transmission, but that trend is reversing.
Because it’s the default port, spammers and malicious actors often abuse it to send harmful messages. Consequently, many internet service providers (ISPs) and cloud hosting providers have blocked this port, making it unsuitable to use.
This port was adopted in 1997 by the IANA. It was aimed to allow users to send encrypted messages via the Secure Sockets Layer (SSL) protocol. However, SSL was later deprecated in favor of the Transport Layer Security (TLS) protocol. Consequently, the 465 port was deprecated, and most email service providers (ESPs) no longer support it.
Some old ESPs still support this port, but in general you should refrain from using it because your messages may not reach the intended recipients if the option is no longer supported.
This port was released in 1997 alongside 465. It allows users to secure their connection using TLS, if both parties support this option, or fallback to unencrypted transfer if not. It is the standard and most secure port for email transmission. Most ESPs and ISPs support this port, making email delivery seamless. 587 should always be your first choice.
This port is a suitable alternative if 587 is not available. This case is tricky, as 2525 is not officially recognized as an SMTP port by the Internet Assigned Numbers Authority (IANA) and Internet Engineering Task Force (IETF). Yet, many ESPs will still support it.
We have explained how SMTP works to send messages between mail servers. Ports allow this process to happen, and we’ve described the different SMTP ports and outlined which ones you should use or not use. At this point, you probably understand SMTP ports enough to explain to someone else.