Mail relay port

A mail relay port is a network port used to forward email messages between mail servers. It is a critical component of the Simple Mail Transfer Protocol (SMTP) and is used to route email messages between mail servers, allowing them to be delivered to their final destinations.

In an email system, a mail relay port is typically used to forward email messages between mail servers, rather than directly between the sender's and recipient's mail servers. This is because mail servers are often configured to only accept email messages from specific IP addresses or domains, and may not be able to accept messages from unknown or untrusted sources.

Here's how it works:

1. An email client (such as a desktop email program or a web-based email service) sends an email message to a mail server (also known as a Mail User Agent or MUA).
2. The mail server forwards the email message to a mail relay server (also known as a Mail Transfer Agent or MTA), which is configured to accept email messages from the mail server.
3. The mail relay server forwards the email message to another mail relay server, which is configured to accept email messages from the previous mail relay server.
4. This process continues until the email message reaches the final mail server, which is configured to deliver the email message to the recipient's email account.

Mail relay ports are typically used in the following scenarios:

1. To route email messages between different mail servers or domains.
2. To filter or block spam or unwanted email messages.
3. To provide a layer of security and authentication between mail servers.
4. To allow email messages to be forwarded to multiple recipients or domains.

Common mail relay ports include:

• Port 25: The standard SMTP port used for email message transmission.
• Port 587: The submission port used for email message submission from email clients to mail servers.
• Port 2525: An alternative SMTP port used for email message transmission.

It's worth noting that mail relay ports can be used for both legitimate and malicious purposes. For example, spammers may use mail relay ports to send large volumes of spam email messages. As a result, mail relay ports are often subject to strict security controls and regulations to prevent abuse.