Steps to Set Up SMTP Relay

1. Configure your device or application with the following settings:

   Expand Table

   Device or Application Setting	Value
   Server/Smart Host	Your MX endpoint (e.g., contoso-com.mail.protection.outlook.com). Refer to the MX record guide.
   TCP Port	25
   TLS/StartTLS	Enabled (TLS 1.3 or TLS 1.2)
   Email Address	Any email address in a verified accepted domain in Microsoft 365 or Office 365 (no mailbox required).

2. Create an IP address-based inbound connector in Microsoft 365:

   If you already have an inbound connector (e.g., for a hybrid environment), a dedicated SMTP relay connector may not be necessary.

   1. In the Exchange Admin Center (EAC), navigate to Mail Flow Connectors, or go directly to Connectors.

   2. On the Connectors page, click Add a Connector.

   3. In the New Connector wizard, set:

      • Connection from: Your organization's email server
      • Connection to: Office 365 (default, unchangeable)

      

      Click Next.

   4. On the Connector Name page, configure:

      • Name: Enter a unique, descriptive name.
      • Description: Add an optional description.
      • What to do after saving?:
        • Ensure Turn it on is selected.
        • Ensure Retain internal Exchange email headers is unchecked.

      Click Next.

   5. On the Authenticating Sent Email page, choose By verifying the IP address matches one belonging to your organization, then enter the public IP address.

      

      Click Next.

   6. On the Review Connector page, verify settings. Edit if needed using Back, then click Create Connector.

3. To prevent emails from being marked as spam, add the IP address to your domain’s SPF record. See SPF setup guide.

4. Test the setup by sending an email from your device or application and confirming receipt.