Office 365 Smtp Relay Settings

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Office 365 Smtp Relay Settings – Office 365 provides a great free SMTP relay for sending email to the outside world. If you have a domain in the cloud, you can configure an SMTP relay in Office 365. This can be an Exchange Hybrid configuration or a Microsoft 365/Office 365 cloud configuration. In this article, we will see how to set up an SMTP relay for Office 365.

Let’s see how to configure Exchange Online connectors for devices and on-premises applications for SMTP relay.

Office 365 Smtp Relay Settings

Office 365 Smtp Relay Settings

Go to or any other website that shares your public IP address. Note the Public IP address as you will need it in the next step.

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Note: Get the public IP address of the organization you want to send email to. This can be multiple IP addresses.

An MX record is what you add to a scanner or application that needs to send SMTP using Office 365.

To send via Office 365 SMTP, you must open port 25 of your organization’s firewall to the outside. The safest way is to simply add the Exchange Online IP address to the destination address and not

Log in to your domain registrar and open your domain’s DNS settings. In our example, the domain

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Edit the existing SPF record and add the Public IP address. This effect will also allow the organization’s Public IP address server to send email for the domain name.

Note: Changes can take up to 24 hours, but usually, they will be completed within 5-15 minutes.

Select By verifying that the IP address of the sending server matches one of the following IP addresses, which are exclusively owned by your organization.

Office 365 Smtp Relay Settings

You have successfully added the SMTP relay connector to Office 365. As a result, your organization is ready to send email through Office 365.

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Test that everything is set up correctly and that the email is successfully sent through Office 365. A good way to test the Office 365 SMTP relay is to use the Send-EmailOffice365.ps1 PowerShell script.

Run PowerShell as an administrator. Copy the script below or download the Send-EmailOffice365.ps1 PowerShell script. Before running the script, change the fields:

The output should not give an error, and the email will arrive in the inbox added in the To field.

You have learned how to configure SMTP relay in Office 365. Microsoft gives you a great way to send emails through Exchange Online in Office 365, and you don’t have to pay extra. However, remember to follow these steps. Otherwise, the email will fail to deliver or arrive in SPAM instead of the recipient’s inbox.

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ALI TAJRAN is an IT Architect, IT Consultant, and Microsoft Certified Trainer. He started Information Technology at a young age, and his goal is to teach and inspire others. Read more »The current article is dedicated to the topic – solving problems that can occur when using an SMTP email relay server to send emails in the Office 365 mail infrastructure.

In the previous article, we examined the concept of how to configure an IIS SMTP server as a mail relay in an Office 365-based environment.

Office 365 Smtp Relay Settings

When using the SMTP mail relay option in an Office 365 environment, the mail flow can be considered complex because there are several elements involved in this process, and each of these elements has specific characteristics or specific configuration settings.

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In the scenario where we have a problem definition, the mail sent by the source mail client (Hardware device, mail application etc.) does not reach the destination (Office 365 receiver or other external receiver), the ability to determine the exact cause. of the problem is not so simple.

For example, a scenario where a FAX device needs to send an E-mail message to an Office 365 recipient includes the following steps:

Actually, the mail flow includes additional steps that we haven’t mentioned yet such as doing the DNS resolution process and so on.

Because of this complexity, we need to understand the various components that are in the mail flow and what are the troubleshooting steps, troubleshooting tools and methods that can be used in situations where the mail flow is completed successfully.

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Once we have completed all the necessary configurations, the best practice is to implement some “POC” (proof of concept) testing; which will allow us to verify that the mail flow has been implemented correctly, ie the E-mail message has successfully reached the recipient’s mailbox.

To test and verify mail flow when using SMTP mail relay, we will simulate a mail flow where an organization’s mail client tries to send an E-mail to an Office 365 mail recipient.

Test 1 – a simple test where we simulate a mail client using the same E-mail address as the user credentials used by the SMTP IIS mail relay server.

Office 365 Smtp Relay Settings

Test 2 – impersonate a mail client, using a different E-mail address than the user credentials used by the IIS SMTP mail relay server. In that case, we want to verify that the required Send As permission is specified for the IIS SMTP email relay server user account.

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In our scenario, the “real” mail client can be a hardware device such as a FAX machine, Scanner or Printer or a mail-enabled application.

The main problem is that usually, these “mail clients” do not have the option to provide accurate information in the failure scenario, meaning the scenario where the email is not delivered to the intended recipient.

To get a clear view of the mail flow process, I recommend a very good SMTP mail client utility called: Basic SMTP Telnet Client.

The Basic SMTP Telnet Client utility allows us to synchronize the mail flow and “see” the contents of the communication channel between the mail client and the mail server (the IIS SMTP mail relay in our scenario). In addition, we can use the “debug” option (enable step-by-step transmission) to obtain information about the specific cause of the problem.

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In the first test, we want to verify that the mail flow has completed successfully, meaning that each of the different “elements” involved in the mail flow can communicate with each other.

In our scenario, the email client will identify itself using the same E-mail address as the user credentials used by the IIS SMTP email relay.

Regarding the subject of “destination recipient” in the target E-mail address, the recipient does not matter as long as we have the ability to access the mailbox of the target recipient and verify that they received our test mail.

Office 365 Smtp Relay Settings

In the next section, we will use the basic Telnet SMTP Client utility to simulate mail flow from an internal mail client.

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The Telnet properties tab is used, to configure communication settings on the internal interface of the IIS SMTP mail relay server.

To send an E-mail message we must select the Telnet tab and click the SEND option

In the image below, we can see that the “first part” of our mail flow, the part where the internal mail client addresses the internal interface of the SMTP IIS email relay is completed.

IIS SMTP email relay “agrees” to receive E-mail messages and “notifies” email clients if –

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The fact that the first part of the mail flow is successfully completed does not mean that we can assume that the E-mail message has reached the destination mailbox of the Office 365 recipient.

To verify that the E-mail was sent by the IIS SMTP mail relay to the Office 365 mail server (EOP represented by the host name we must access the mailbox of the intended recipient (John in our example) to verify that he received the message E-mail.

Test 2 – Verify the SMTP mail relay’s ability to send emails on behalf of different mail clients.

Office 365 Smtp Relay Settings

In case the first test has been completed successfully and, we know that the mail flow has been configured correctly, the next step is to verify the ability of the IIS SMTP mail relay to send email messages on behalf of various other mail clients.

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For example, the basic assumption is that every email client that will respond to an IIS SMTP email relay server will identify itself using a unique E-mail address.

The IIS SMTP email relay server identifies itself to the Office 365 mail server using a specific user account ([email protected] in our scenario) and sends mail on behalf of other mail recipients; user account of the IIS SMTP email relay server, must be configured with the Send As permission for each email client that will “forward” its requests to the Office 365 mail server.

Note that in this type of scenario, the IIS SMTP mail relay must have the “Send As” permission which allows it to send E-mail messages on behalf of the source.

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