Billions of emails pass through the Internet every day. However, most people aren’t aware of the inner workings enabling this massive information exchange.
The SMTP protocol is a core set of rules that allows emails to flow freely. To set up SMTP properly, you need to understand SMTP port numbers and learn how to choose the best port for transmitting emails.
What Is SMTP?
It is an abbreviation for Simple Mail Transfer Protocol. It is a protocol for transmitting emails between servers. Whenever you send an email, you’re transferring information from your server to the recipient’s server. SMTP is a set of rules that ensures the mail gets to the correct server and final recipient.
An SMTP port is the number a computer uses to route the incoming data to the correct application (in our case, to an SMTP server app). Choosing a proper port number is an important part of SMTP setup.
How Does SMTP Work?
Here’s a brief explanation of what happens when you hit the send button on your mail client.
- Your mail client connects to its assigned SMTP server using the server address and port number.
- The client submits the sender’s and recipient’s email addresses to the server along with the message’s contents.
- The server checks if the sender’s and recipient’s addresses share the same domain name (and IP address). If so, it sends the message directly to the recipient’s server. If not, it queries the domain name system (DNS) to identify the IP address of the recipient’s server and sends the message there.
- The receiving server verifies the data and sends the incoming message to the final recipient’s mailbox.
The entire process typically occurs within seconds of hitting the send button.
SMTP Ports
SMTP ports are identified by decimal numbers, like 25, 587, 465, or 2525. Applications may use different ports, but some of them have their own peculiarities.
When setting up an SMTP connection, you must consider which ports to use. Otherwise, you may face problems sending messages effectively.
25
This one is the oldest, established back in 1982, and it’s used for unencrypted plain text connections. This port was often abused to send spam and malicious messages. Hence, now many email service providers don’t support it at all.
587
This is the default port for secure mail submission, and generally the best choice. It lets you submit messages securely and ensure they are not compromised.
465
This port was registered in 1997 for secure mail submission but was deprecated later on and is no longer an accepted standard. It’s not advisable to use this port because it has been phased out, even though many ESPs still offer it.
2525
This is an alternative port to 587 for secure email submission. It’s not technically recognized as an official SMTP port, but many email service providers support it.
As shown above, 587 and 2525 are the best ports for sending emails. Any email service provider you choose should support these ports.
25 is unsuitable because it’s often abused for malicious purposes, and 465 is not recommended because it has been deprecated by the Internet Engineering Task Force (IETF) and Internet Assigned Numbers Authority (IANA), the two agencies overseeing the Internet standards.
Choosing an Email Service Provider
You can either operate your own SMTP servers or use external ones offered by email service providers. Using external servers is often preferable because the email service provider takes care of their maintenance and security. In contrast, maintaining and securing your own servers can be stressful and distract you from your core business operations.
UniOne is a good example of a secure and reliable SMTP server provider. It allows you to send bulk messages securely and quickly. It maintains your email infrastructure letting you focus on interacting with customers and expanding your business.