How to Setup Office 365 SMTP Relay: Quick Guide

An Office 365 SMTP relay allows you to send emails reliably from your devices and applications, ensuring your messages reach their destination without being flagged as spam. It’s a handy solution for small businesses, marketers, and sales teams needing to send email using printers, scanners, or third-party email servers.

This guide walks you through how to set up an SMTP relay in Office 365 step by step. From verifying your domain to configuring connectors and troubleshooting errors, we’ve got you covered. By the end, you’ll have a seamless system to relay emails through Microsoft 365 or Office 365, keeping communication smooth and professional.

What Is an Office 365 SMTP Relay and Why Do You Need It?

An SMTP relay in Office 365 is a method to send email through your organization’s devices or third-party applications using the Microsoft 365 SMTP server. This setup helps route outgoing emails via smtp.office365.com, ensuring they adhere to security standards and reduce the chances of being flagged as spam.

Why Businesses Use SMTP Relay

• Reliable Email Delivery: Emails sent via SMTP relay are authenticated and routed through secure Office 365 SMTP settings, which reduces spam risks.
• Supports Bulk Email Sending: Unlike direct email sending, an SMTP relay can handle high volumes, making it perfect for marketing campaigns or system notifications.
• Ease of Integration: Devices like printers, scanners, and applications can be configured to send email using Office 365 SMTP relay without needing individual mailboxes.

How Does SMTP Relay Work?

• Your device or application connects to the Office 365 SMTP server using a verified domain and optional SMTP authentication.
• Emails are sent to recipients using smtp.office365.com as the relay point.
• The SMTP relay authenticates the email source and relays the message to the destination.

SMTP relay is crucial for businesses relying on automated emails. With proper configuration, you can streamline communication while maintaining security and compliance.

Key Requirements Before Setting Up an SMTP Relay

Before configuring your Office 365 SMTP relay, there are a few things you need to prepare. These prerequisites ensure the setup process goes smoothly and avoids errors when sending emails through the relay.

What You Need to Get Started

1. Office 365 or Microsoft 365 Subscription
   • A valid subscription is necessary to access Exchange Online features and configure SMTP relay.
   • Your domain must be registered and verified in Microsoft 365 or Office 365 settings.
2. Static IP Address
   • A static IP address for your device or application is required to identify and authenticate your emails.
   • This ensures your relay traffic comes from a trusted source.
3. Relay Device or Application
   • A printer, scanner, or email application capable of using SMTP relay to send emails is essential. These devices must support connections to smtp.office365.com.
4. Network Configuration
   • Ensure your network allows outbound traffic on Port 25 (or other specified ports). Port 25 is commonly used for SMTP relay traffic.
5. Connector Setup in Office 365
   • You’ll need to create a connector for SMTP relay in the Microsoft 365 admin center to authenticate and route your emails securely.
6. Authentication Method
   • Choose between certificate-based authentication or basic authentication depending on your organization’s security policies. Modern setups may prefer SMTP authentication for enhanced security.

These requirements form the foundation for setting up a seamless SMTP relay in Office 365. Missing any of these can lead to issues such as emails not sending or being marked as spam.

Step-by-Step Guide to Setting Up an Office 365 SMTP Relay

Here’s how to configure an SMTP relay in Office 365 step by step. Follow these instructions to ensure your devices or applications can reliably send email using Microsoft 365.

Step 1: Verify Your Domain in Office 365

Before using SMTP relay, your custom domain must be verified in Microsoft 365 or Office 365 settings:

1. Log in to the Microsoft 365 admin center.
2. Go to Settings > Domains.
3. Add your domain and follow the prompts to verify ownership.
   • Use the DNS settings provided to create TXT or MX records in your DNS host.
4. Once verified, you can configure your domain to use SMTP relay.

Without domain verification, Office 365 SMTP server won’t authenticate your emails, and they might be blocked.

Step 2: Configure an SMTP Relay Device or Application

Now, set up your device or application to send emails via the SMTP relay:

1. Access your device or application’s email configuration settings.
2. Enter the following SMTP server details:
   • SMTP Server: smtp.office365.com
   • Port: 25 (ensure your network supports it).
3. Use your static IP address as the sending device.
4. Disable SMTP authentication (since SMTP relay uses IP-based authentication).

This step allows your device to relay emails on your behalf. If using basic authentication, ensure credentials are configured correctly.

Step 3: Set Up a Connector in Office 365

To ensure secure communication, you need to create a connector for SMTP relay in Microsoft 365:

1. Open the Exchange Online Admin Center.
2. Navigate to Mail Flow > Connectors.
3. Click + Add a Connector and choose:
   • From: Your organization’s email server
   • To: Office 365
4. Provide your device’s static IP address for IP-based authentication.
5. Enable TLS encryption for secure relay traffic.

This connector to relay email ensures your messages pass through Office 365 SMTP relay securely.

Step 4: Test the SMTP Relay Configuration

Finally, test the setup to confirm everything works:

1. Send a test email from your device or application.
2. Verify the message is delivered to the recipient without issues.
3. Check logs or reports for any errors, such as authentication failures or blocked emails.

If you encounter issues, revisit your SMTP server settings or troubleshoot the connector.

Common Challenges and How to Overcome The

Setting up an Office 365 SMTP relay can sometimes come with challenges. Below are common issues and practical solutions to resolve them.

1. Emails Are Marked as Spam

Problem: Emails sent through the SMTP relay end up in the recipient’s spam folder.
Solution:

• Configure email authentication protocols like SPF, DKIM, and DMARC in your domain’s DNS settings.
• Verify that your static IP address is not listed on any spam databases.
• Avoid using generic email addresses like noreply@example.com for sending mail.

2. Authentication Failures

Problem: The SMTP relay cannot authenticate the sending source.
Solution:

• Ensure the connector in Microsoft 365 is correctly configured to allow relay emails from your device’s IP address.
• If using SMTP authentication, verify credentials are accurate and basic authentication is enabled if required.
• For modern setups, use certificate-based authentication or OAuth2 where applicable.

3. Port 25 Blocked by ISP

Problem: Outbound traffic on Port 25 is restricted by your internet service provider.
Solution:

• Request your ISP to unblock Port 25, or use alternate ports (if supported by your SMTP server).
• Check if your network firewall rules allow SMTP traffic through the port.

4. High Email Bounce Rates

Problem: Many emails fail to reach their destination due to relay misconfigurations.
Solution:

• Check that the connector in Office 365 is correctly set up for IP-based authentication.
• Verify the email addresses being sent to are valid and active.
• Monitor logs for detailed error messages.

5. Configuration Errors in Devices or Applications

Problem: Your device or application isn’t properly configured to use SMTP relay.
Solution:

• Double-check the SMTP settings:
  • Server: smtp.office365.com
  • Port: 25
  • TLS: Enabled
• Ensure the device supports email relay functionality and complies with Microsoft 365 requirements.

By addressing these common issues, you can ensure smooth operation and reliable email delivery through your Office 365 SMTP relay

Best Practices for Using Office 365 SMTP Relay

A properly configured SMTP relay not only improves email reliability but also strengthens your communication system. Here are some best practices to ensure optimal performance and security when using an Office 365 SMTP relay.

1. Use Strong Email Authentication Protocols

• Set up SPF (Sender Policy Framework) to specify which servers are authorized to send emails for your domain.
• Enable DKIM (DomainKeys Identified Mail) to add a digital signature to your emails, ensuring their authenticity.
• Implement DMARC (Domain-based Message Authentication, Reporting, and Conformance) to prevent email spoofing.

These measures protect your domain reputation and reduce the chances of emails being flagged as spam.

2. Monitor Email Logs and Reports

• Regularly review email logs in the Exchange Online Admin Center.
• Look for errors, such as failed deliveries or authentication issues.
• Use reports to identify unusual sending patterns that might indicate misuse.

3. Avoid Using Public IPs

• Always configure your relay to use a static IP address.
• Public IPs can cause security risks and lead to email delivery issues.

4. Set Up Alerts for SMTP Relay Failures

• Configure alerts in Microsoft 365 to notify you of issues with the SMTP relay setup.
• Early detection helps resolve problems before they disrupt communication.

5. Stay Within Sending Limits

• While SMTP relay offers higher sending limits than SMTP client submission, excessive bulk emails may still trigger throttling.
• Use distribution lists or segment email campaigns to manage volume efficiently.

6. Regularly Update Security Settings

• If using basic authentication, plan to switch to modern alternatives like OAuth2 to align with Microsoft’s deprecation roadmap.
• Use a certificate-based connector in Microsoft 365 for added security when possible.

By following these practices, you can maximize the efficiency and security of your Office 365 SMTP relay setup.

FAQs

Conclusion

Setting up an Office 365 SMTP relay can significantly improve the way your business communicates. It ensures reliable email delivery for your devices and applications while maintaining security and compliance with Microsoft 365 standards.

By following the steps outlined in this guide—verifying your domain, configuring devices, setting up a connector, and testing the setup—you can enable seamless email sending through smtp.office365.com. Adopting best practices, like using strong email authentication protocols and monitoring email logs, ensures long-term success and avoids common pitfalls.

Whether you’re a small business owner managing notifications or an enterprise team handling bulk emails, a properly configured SMTP relay makes it all possible. Start optimizing your email system today and stay ahead in your communication game!