How to use telnet to communicate with a smtp server

HOW TO USE TELNET TO COMMUNICATE WITH A SMTP SERVER HOW TO
HOW TO USE TELNET TO COMMUNICATE WITH A SMTP SERVER WINDOWS

The procedures in this topic are best used to connect to and from Internet-facing servers that allow anonymous connections. These procedures are performed in the operating system of the Exchange Server or a client computer. What do you need to know before you begin?Д®xchange permissions don't apply to the procedures in this topic.

HOW TO USE TELNET TO COMMUNICATE WITH A SMTP SERVER WINDOWS

Third-party Telnet clients may require a syntax that is different from that of the Windows Telnet component.

HOW TO USE TELNET TO COMMUNICATE WITH A SMTP SERVER HOW TO

The procedure in this topic shows you how to use Telnet Client, which is a component that is included with Microsoft Windows. Here are the scenarios where you may want to use Telnet to test SMTP communication to or from the transport servers that exist in your Microsoft Exchange organization:Д¬onnect to your organization's Internet-facing Exchange server from a host that is located outside your perimeter network and send a test message.Д¬onnect to a remote messaging server from your organization's Internet-facing Exchange server and send a test message. You can see the success or failure of each step in the connection and message submission process. If you use Telnet on port 25, you can enter the SMTP commands that are used to connect to an SMTP server and send a message exactly as if your Telnet session was an SMTP messaging server.

The deal with the STARTTLS way to do smtp is to use the two well known originally plain-text tcp/25 and tcp/587 ports, and only when the initial clear-text connect suceeded, to then START the TLS layer (thus STARTTLS) from there on, having a secured connection from that point onwards.ДЄs for debugging these kind of things maybe via command-line tools, for example for windows there is the historical blat command line mailer (smtp), which up till today cant do TLS (STARTTLS) so it can only use plain-text smtp to send its mails.This topic explains how to use Telnet to test Simple Mail Transfer Protocol (SMTP) communication between messaging servers. Tcp/587 was intended as a replacement to default tcp/25 port initially when spammers and mass mailing attacks commenced like a decade or more ago, but also during those infamous AOL ages, when some funny ISP had some blocks on default ports outbound (such as that tcp/25) for denying their own customers (AOL) to mass-send emails/spam back then, but AOL-customers needing to use alternative mail-accounts and mail-providers still needed to send their mails from AOL-internet connections, so they could still connect to tcp/587 and do simple smtp on it back then. Tcp/465 was initially intended for establishing the SSL(and newer TLS) layer first, and inside doing cleartext or plain old protocols (smtp here) So, this should look like the following: ^M Just pressing the 'ENTER' key does not apparently result in a CRLF which SMTP needs to end a message. There is one more oddity to overcome if you're using OSx or Linux terminals. Do the same for your password, which is requested next. Using a Base 64 encoder such as this one, encode your user name and enter it. This is essentially the word 'Username' encoded in Base 64. Then, type 'auth login' and you will receive the following: 334 VXNlcm5hbWU6 Perhaps someone with more knowledge can explain. I don't know much about SMTP so I cannot explain the difference, and don't have time to research much.

ДЄnd you'll receive: 250 mx. at your serviceДЇrom there it is not quite as straightforward as just sending SMTP messages because Gmail has protections in place to ensure you only send emails appearing to be from accounts that actually belong to you.

You should get lots of information on the SSL session and the response: 220 mx. Also, I don't believe you want to use -starttls smtp openssl s_client -connect :465 25 is the generic SMTP port, but not what GMail uses. Using Linux or OSx, do what Sorin recommended but use port 465 instead.

How to use telnet to communicate with a smtp server