What Is Simple Mail Transfer Protocol (SMTP)?

SMTP stands for Simple Mail Transfer Protocol and is the procedure behind the email productivity on the Internet. There are many people who constantly send out emails but haven’t a clue how they reach their destination. SMTP literally puts into action a process that is similar to the delivery of mail through the post office. The server or computer that is running SMTP is the mail carrier on the Internet. Messages are directly sent to the SMTP service and then are sent on to their receivers.

Telnetting is an application layer protocol used on the Internet to provide bi-directional interactive test-oriented communication using a virtual terminal connection.

What can be tested by simply telnetting into an SMTP server:

To find out if a server is working.

Whether a firewall blocking communication.

Will a mail server allow for relaying of a certain domain or an email address.

The time it takes for a server to respond.

Whether a server is responding with the correct host name.

Manually testing SMTP in a telnet session:

As a telnet client, you must be verified for installation on the server. Once done, you should find a mail server to sign into. You will need the DNS MX record for a specific domain in order to proceed. You can use commands such as:

Windows:

nslookup -type=mx mailtrap.io

Linux:

nslookup -type=mx mailtrap.io

Non-authoritative answer:

Server:             192.168.0.1

Address:          192.168.0.1#53

In order to use the IP, you need the DNS PTR so start with the IP address that the Internet recognizes you have. You can use: http://whatismyipaddress.com/ to get this information.

Once you get your IP address run a command with T.T.T.T standing for the IP address.

Windows:

nslookup -type=ptr T.T.T.T

Linux:

nslookup -type=ptr A.B.C.D

Server:             192.168.0.1

Address:          192.168.0.1#53

Non-authoritative answer:

212.235.118.46.in-addr.arpa   name = SOL-FTTB.212.235.118.46.sovam.net.ua.

There are now two requirements; the MX record for railsware.com and the PTR for the IP you will be using. Now you can log in to the SMTP server and this is the command:

telnet mail.railsware.com 25

You will see something like the following code:

Trying 45.55.56.249…

Connected to mail.railsware.com (45.55.56.249).

Escape character is ‘^]’.

220 mail.railsware.com (PowerMTA(TM) v4.0) ESMTP service ready

The first command to the mail server is going to be EHLO or HELO, which is a basic greeting that initiates the communication between the SMTP server and the telnet client.

EHLO server.example.com

The next step is going to be the MAIL FROM. This command will define the address which bounces are delivered. The “From” header is not the same thing:

MAIL FROM: <test@railsware.com>

250 2.1.0 MAIL ok

Now that you have the MAIL FROM command, you can send the RCPT TO. This command will determine who the message should be sent to. This is similar to MAIL FROM except will be MAIL TO in the header.

RCPT TO: <test@railsware.com>

250 2.1.5 <test@railsware.com> ok

Before starting the body of your message you should run the DATA command. This command will explain all the other content.

Some mail servers support Pipelining. That means the SMTP will wait until the DATA command is sent before responding to other commands So, enter the MAIL FROM, RECPT TO, DATA commands before waiting for a response.

At the beginning, define the address of a SMTP server. Use a ns lookup command or another online service.

END…. THIS IS JUST NOT WORKING

• Tags:

COMMENTS.

comments