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SMTP Relay Explained

There are many different people who have a hard time understanding the concept of SMTP relay. There are some people who are too cautious and may block every relay email delivery completely out. There are still others who leave their SMTP servers completely open. Either action will cause problems for the person’s mail server. Because either action is not acceptable for men and women who want to keep their SMTP email server open it is better to understand what relay is. It is also better to understand how to configure the SMTP host server so that it is no longer vulnerable to any potential outside attacks while still being able to send and receive emails for trustworthy users.

SMTP Explained

SMTP-Relay-ExplainedSMTP is an acronym used for the term Simple Mail Transfer Protocol. Nearly all internet providers use the SMTP service to send different emails. In addition, different email clients will use this protocol in order to act as an SMTP cloud email client to send different emails to their respective recipients. When clients send their messages, it will connect to an SMTP server that has been configured. It will than communicate to that server using the Simple Mail Transfer Protocol.

The mail SMTP service is best described as a local post office. The users who wish to send an email will send it to the SMTP server. That server will then forward it to the recipient’s server. Different recipients use different email addresses in order to ensure that the email goes to them. Every SMTP email server is designed to handle multiple domain names.

SMTP Relay Servers

Open relay can be complicated at times. When one company wants to send an email to another company that company will need to connect to the relay server. That server will relay the message to the server that the other company owns. When there is another server involved that accepts the message that is meant for the company’s server it is known as relaying the message. If every server suddenly stopped relaying messages for other servers, there would be no email deliverability.


Most servers will ask for the email user’s information. This will normally be the user’s ID and password and is required in order to get access to the mail SMTP service. Entering the ID and password will allow the server’s users to relay their message to a different server. He or she will only get access if the credentials are right. Asking for authentication ensures that there will not be anyone outside of the company who can use the company’s SMTP server to send any messages that could harm the company or the server.

Open Relay

Servers that are open relay servers will accept any messages from any other domain without asking for a user’s authentication information. This is dangerous for the user’s company and his or her server. There are many different hackers and spammers who will take advantage of the open server and send unsolicited emails to many different recipients. In fact, it is possible for a spammer to send out millions of emails to millions of men and women all over the world. This would affect the name of your company while potentially crashing your server as well. In addition, there are organizations with various databases full of the IP addresses of open relay servers. If your server is on that list, other SMTP servers will not accept any of your emails. You can find out if your server is an open server by sending an email to your server without using your ID or password. Remember to use a program like Netscape Messenger or MS Outlook.

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SMTP Relay Explained

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