DNS and Networking Tools

How to use SMTP commands

1. Open telnet session to the mail server with port 25 (SMTP):

# telnet mail.example.com 25
220 mail.example.com ESMTP

2. Type the helo command with your domain name:

# helo yourdomain.com
250 mail.example.com

3. Type the sender e-mail address:

# mail from: yourname@yourdomain.com
250 2.1.0 Ok

4. Type the recipient e-mail address:

# rcpt to: webmaster@example.com
250 2.1.5 Ok

5. Type the data command to start enter the mail body:

# data
354 End data with .

6. Type the message body text:

# this is a test

How to verify your mail server public IP address

Many mail servers, even those with an external IP address, route mail through a firewall or proxy server.
From the perspective of any external mail servers, the firewall or proxy IP address is connecting to external mail servers, not the other mail server.
If you are unsure whether you are sending through a firewall or proxy server, the following test will show the path of any mail that leaves your system.
Automatic Process:

How Domain Name Servers Work

If you spend any time on the Internet sending e-mail or browsing the Web, then you use domain name servers without even realizing it. Domain name servers, or DNS, are an incredibly important but completely hidden part of the Internet, and they are fascinating.

The DNS system forms one of the largest and most active distributed databases on the planet. Without DNS, the Internet would shut down very quickly.

In this article, we'll take a look at the DNS system so you can understand how it works and appreciate its amazing capabilities.