Most businesses and individuals use email as one of the communication methods between clients, running marketing campaigns, and raising brand awareness. But what ensures that your email reaches your recipient?

When emailing, SMTP ensures the transfer of email data through the internet from one server to another.

What is an SMTP port?

SMTP is sending emails through the internet.

Email clients use SMTP to help upload messages to the outgoing mail servers that pass the information to the recipient's incoming mail server.

Mail servers, like web servers, require domain names and IP addresses to know where to send the message. While the IP address identifies the computer, a port identifies the specific application or service running on the computer.

Why does the SMTP port matter?

When submitting an email from one email client to another, there are stages involved in the transmission. Different SMTP ports come into play to ensure the delivery of the message.

If you are setting up an SMTP service, chances are that your focus is on the submission part of the process that ensures the relaying of the email message to the outgoing mail server. Port 587 is, in most cases, used during submission.

When submitting the email to the outgoing mail server, the outgoing mail server relays the information to the recipient's mail server. Transferring the information between servers requires a different port from that used during submission. You will need to use port 25 for you to deliver emails.

Why you should use different ports for different SMTP purposes

While there are multiple SMTP ports, not all work in all situations. We employ various ports to submit and relay messages.

Default ports

Port 25 is the standard port for moving messages between servers, although ISPS and cloud services often block it for being known as the popular port used by spammers on the internet.

After establishing a connection between different mail servers, the server determines whether a message intends to be delivered to the mail server or submitted to a new SMTP. Having other ports allows administrators to add restrictions during each kind of interaction.

What are popular mailserver ports in use?

Port 25

In 1982, port 25 made its first debut after being published by the IETF as the standard and default channel for email transmission on the internet.

Despite being the default SMTP port used to submit emails, it's not used because it isn't secure and is used to send spam emails and malware.

Port 465

According to the IANA, SMTP shouldn't use port 465 for communication. The purpose was to provide a port for SMTP to operate using the SSL, typically used to encrypt communication on the internet.

It is not recommendable to use this port as many ISPS block it.

Port 587

It is the default port for email submission paired with TLS encryption that ensures they submit secure emails according to the IETF guidelines.

Port 2525

It is an alternative for port 587 as it supports TLS encryption.


When picking the right SMTP port consider which ports your server or recipients server support. Many servers support a range of ports but you will need to test each port to see if it can connect.