Send Mail Using Telnet Smtp

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Send Mail Using Telnet Smtp – In this article, we’ll look at the mail flow scenario where external hosts, such as a web application or email-enabled devices, contact an Exchange Online server through a standard SMTP session.

In the past, the primary way to approach the Exchange Online server was by using the TLS protocol + providing user credentials.

Send Mail Using Telnet Smtp

Send Mail Using Telnet Smtp

This requirement presents a major difficulty for “external hosts” that need to use Exchange Online services as an email server, as often the external host did not have the ability to support the TLS protocol or provide certain user credentials.

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The good news is that we can choose an “easy way” that will allow the external host to reach the Exchange Online server and request mail services without complex configuration.

The only condition we must meet is to allow Exchange Online to identify the “external host” by providing Exchange Online with that host’s public IP address.

The “identification mechanism” is implemented by creating an incoming mail connector that will include the IP address used by external servers that address the Exchange Online server.

In the following diagram, we can see a logical representation of the mail channel between an external mail-enabled server (web application, printer, fax machine, etc.) and an Exchange Online server.

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Note that external hosts can contact the Exchange Online server to ask it to deliver an email message to Office 365 recipients or to an external recipient (non-Office 365 recipients).

It is important to be able to distinguish between the logical channel and the “physical channel”. In reality, mail-enabled servers do not go directly to Exchange Online, but through a gateway such as firewalls.

In other words, in fact, when mail activates the host address of the Exchange Online server, the external hosts are represented by the public IP address that the firewall uses.

Send Mail Using Telnet Smtp

As mentioned, to allow Exchange Online to identify external mail, you enable the host so that Exchange Online can “trust” it and provide them with the necessary mail services. The Exchange Online server must be preconfigured with specific IP address information to be used by external email-enabled hosts.

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In the diagram below, we can see an example of a scenario where the firewall “presents” multiple mail-enabled hosts.

Exchange Online does not need to “know” the internal IP address of this host or the specific IP address of any email-enabled host.

Instead, the Exchange Online server will only know the public IP address used by the firewall server that represents the particular network.

In this article, we refer to the Office 365 mail server “entity” as the Exchange Online server. If we want to be more precise, the “real object” we are referring to is the EOP (Exchange Online Protection) server.

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The EOP server is the mail gateway and mail security gateway that represents the Office 365 mail infrastructure.

The mail flow configuration where our mail-enabled servers will use Exchange Online as their mail server based on the following steps:

Step 1#4: Get the hostname of the Exchange Online server that represents our Office 365 domain.

Send Mail Using Telnet Smtp

There are two ways we can use to get information about the Exchange Online FQDN (Fully Qualified Domain Name) that “sends email for our domain”.

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Another way to get information about the “hostname” of the Exchange Online email server that “represents” our organization is: using the nslookup tool.

In order to configure the necessary Exchange Online incoming mail connector, we will need to prepare in advance the public IP address used by the mail-enabled servers.

In the event that mail-enabled external hosts is the host that resides on your network, you can check with the technical contact responsible for the firewall infrastructure which IP address represents the organization.

A simple option that will allow you to find the public IP address that represents a particular desktop or network is to use your browser and enter the query:

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Your import network stresses that this is not a “definitive answer” because in many scenarios the network is represented by more than one public IP address.

In a scenario where the email-enabled server is a web application hosted by an external ISP, check with your ISP and ask them what public IP address or public IP range they are using.

Step 3 #4: Create a new Exchange Online Inbox connector that identifies this host’s IP address as “trusted”

Send Mail Using Telnet Smtp

In the next section, we will provide step-by-step instructions on how to create the required Exchange Online Inbox Connector.

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Metaphorically, we can relate the Exchange Online Inbox Connector as an “ear” that listens for communication request from email-enabled servers.

The Description: field is optional, but I recommend adding a detailed description to help us (or other IT members) easily understand the purpose of the Exchange Online mail connector in the future.

In the following screenshot, we can see that we can “authenticate” external mail-enabled hosts using one of the following options.

In our scenario, we need to identify external email-enabled servers using the IP address option.

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Select the option: Verifying that the IP address of the sending server matches one of these IP addresses that belong to your organization

In the following screenshot, we can see the result, the IP address that the Exchange Online server “resolves”.

In the following screenshot, we can see the summary information about the new Exchange Online Inbox Connector.

Send Mail Using Telnet Smtp

Technically speaking, the task of creating the necessary configuration to allow our hosts to reach the Exchange Online server is complete.

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In order to verify that we can implement the communication channel between the source (the mail-enabled hosts) and the destination (the Exchange Online server), we can simulate the communication channel by trying to Telnet from our network (the hosts’ network). mail-enabled hosts) to the Exchange Online server and see if we can establish the necessary communication channel.

In the next section, we will demonstrate how to communicate with the Exchange Online server using a telnet client and a friendly GUI telnet client.

In case you want to test or simulate the communication channel to the EOP server using a “standard SMTP session”, you can try sending email through EOP using a Telnet session.

In the next section, we will demonstrate how to use a Telnet client to verify the communication channel with EOP.

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Note: Telnet client is not installed by default in Windows operating system, you will need to install Telnet client.

In the following screenshot we can see the result, the response from the EOP server is displayed on the screen:

To simplify the testing process, we’ll also use John’s email address as “East Email Address”.

Send Mail Using Telnet Smtp

In simple terms: we will simulate a process where John sends an email to himself by addressing the EOP server.

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To be able to “indicate” to the destination mail server that we want to enter the content of the email message, we use the command: data

In order to “indicate” to the EOP server that we want to end the session and send the email message, we use the periodic letter:

In our example, we see the response from the EOP server. A “Mail Queued for Delivery” message is usually a good sign.

The meaning is that the destination mail server agrees to accept our email message and the email message is queued in the mail server.

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Another way we can use to: Check the SMTP communication channel with Exchange Online and get more detailed information in case of communication failure is a very nice and useful tool called: SMTP Test Tool

Note: The SMTP tester does not come with an installation file, but only an EXE file named: telnet25.exe

In the next section, we will demonstrate how to use the SMTP Tester tool to establish an SMTP session with the Exchange Online server.

Send Mail Using Telnet Smtp

Scenario Description: In our example, we will go to the Exchange Online server that represents the domain name and send the email message from: [email protected] to itself.

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We can assume that the mail delivery has completed successfully because in the log file we can see the information: “Mail queued for delivery”. We use cookies to make it great. By using our site, you accept our cookie policy. Cookie settings

This article was co-written by staff writer Nicole Levine, MFA. Nicole Levine is a technology writer and editor for . He has more than 20 years of experience creating technical documentation and leading support teams at large web hosting and software companies. Nicole also holds an MFA in Creative Writing from Portland State University and teaches composition, fiction writing, and vocational creation at various institutions.

Software like Thunderbird and Outlook make sending email seem like magic. Well, until your email never reaches its destination. How can you find out what’s really going on when you click Send? One way is to send a test message from your email provider’s outgoing server with telnet, a small application that comes with your computer. You may see an error message indicating your email software

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