What is an SMTP port and how to choose the right one

SMTP ports play an important role in Simple Mail Transfer Protocol (SMTP) forwarding. This is why it is important to choose the correct port when setting up an email server. Incorrect settings can lead to errors when sending and receiving emails.

In this article we will describe what SMTP ports are used for and we will talk about four of them. We will also explain its functions and features to help you choose the right port for your SMTP server.

What exactly are SMTP ports used for?

While SMTP is a mail delivery protocol that allows users to send email over the Internet, SMTP ports serve as communication endpoints that handle information transfers from one server to another.

To start using an SMTP server, you have to set up your email account. This can be done by entering an IP address and port number to route your emails correctly.

There are three phases that emails have to go through before reaching the recipient:

Email sending – sending emails to an outgoing mail server. This happens through SMTP, so you will have to decide which port to use.
SMTP Relay – relay messages between two mail servers. Normally, users do not have to configure a port for it, as it uses one by default.
Mail reception – emails arrive at the recipient’s server. This process is handled by the Internet Message Access Protocol (IMAP)/Post Office Protocol 3 (POP3).

What port to use to connect to your mail server?

Each SMTP port supports at least one level of encryption that determines the security of the email transmission process. When choosing a port, make sure you choose the one that best suits your needs.

There are four levels of encryption available:

Secure Ports Layer (SSL). SSL encryption is an outdated technology that protects email transmissions between two SMTP servers.
Transport Layer Security (TLS). TLS is the successor to SSL that encrypts Internet traffic using modern and secure systems.
Opportunistic TLS (STARTTLS). STARTTLS is a protocol command used to convert an insecure connection to a secure one using SSL/TLS.
Null (NONE). Encryption is not provided.

pro tip

In hPanel, you can check your account’s default email settings by navigating to Emails -> Domain name -> Configuration settings.

Use of unencrypted SMTP port 25

Initially, the Internet Engineering Task Force (IETF) assigned SMTP port 25 as the standard transmission channel for email.

Although the Internet Assigned Numbers Authority (IANA) still recognizes it as the default SMTP port, we do not recommend using it as a mail delivery channel. In fact, port 25 has been used to spread spam and malware.

Also, port 25 does not encrypt the messages, transmitting the information in plain text. Since unencrypted data can be intercepted by threat actors, this raises many security concerns.

Because of this, many Internet Service Providers (ISPs) and web hosts have decided to block all traffic on port 25. This is done to reduce the sending of unsolicited emails through it.

That said, port 25 is a good channel for testing your connection or troubleshooting email setup. For example, if the server is not responding using port 25 when configuring your website’s contact form, it indicates a problem other than the SMTP server.

Send mail through SMTP port 465

Port 465 is a better alternative to 25 in case port 587 doesn’t work.

IANA introduced SMTP port 465 as an enhancement to port 25. It facilitates the secure transmission of email using Simple Mail Transfer Protocol over SSL (SMTPS). However, the IETF never officially approved it as an official SMTP port.

Sending mail over port 465 is secured using implicit TLS, which means that the initial connection is encrypted using an SSL or TLS certificate.

Currently, SMTP port 465 is deprecated and is no longer considered an accepted standard for sending mail. We recommend that you use it only if your hosting provider requires the protocol.

Sending messages through SMTP port 587

SMTP port 587 was introduced as a successor to channel 465. Both the IANA and the IETF recognize it as the current default port for sending email.

SMTP port 587 supports STARTTLS, which means it also works with SSL and TLS encryption. It enables secure messaging and provides a layer of protection against spam and malware.

STARTTLS is a protocol command issued between an email program and a server. It encrypts information transmitted over TLS connections. Additionally, STARTTLS offers SMTP authentication which requires the SMTP client to authenticate with the mail server to access the system.

SMTP port 587 is currently the best option and we recommend that you use it for sending email as it provides a stronger security mechanism compared to the other ports.

Test non-traditional SMTP port 2525

Port 2525 is a modern protocol used to connect to SMTP servers. It is considered a secure option as it supports TLS encryption for email transmission.

Today, it is a commonly used port supported by many ESPs, ISPs, and cloud hosting services. In some cases, port 2525 is used to set up virtual private servers (VPS).

Port 2525 is mainly used as a fallback if you have connectivity issues while sending SMTP. If you’re using port 587 but the connection is blocked or refused, try switching to port 2525 instead.

However, port 2525 is a non-standard channel, so it’s not heavily policed by the IANA and IETF: they don’t recognize it as an official SMTP method. Also, some hosting providers do not support it either.

For example, only uses ports 465 and 587 for SMTP forwarding. We stopped supporting port 2525 in 2017.

conclusion

During the email transfer process, different ports are used to send emails to an outgoing mail server and relay messages from one SMTP server to another.

SMTP is a protocol that allows you to send emails over the Internet. Ports, meanwhile, help direct messages to the proper server and serve as communication endpoints between mail servers.

Choosing the correct port is important for you to be able to send emails. Here is a summary of the four SMTP ports:

Port 25 – It does not have a security mechanism and is therefore not recommended for sending emails. Currently, it is used as the SMTP relay port.
Port 465 – this port was intended for SMTPS, since it used SSL encryption. However, the IANA stopped supporting the protocol and replaced it with the STARTTLS cipher.
Port 587 – it is the successor to port 465 and is currently the default transmission channel for SMTP. Port 587 provides secure email transmission using STARTTLS encryption.
Port 2525 – it is an alternate port used when there are connection problems with port 587. However, it is not recognized by the IANA and the IETF as an official SMTP port.

We hope this article has helped you choose the right SMTP port. If you have any questions or suggestions, leave them in the comments section below.

Carolina is a digital marketing enthusiast with experience in content creation, SEO, and social media management. In her free time she likes to read, watch movies and bake.