How to Troubleshoot Microsoft 365 SMTP Scanning from a Printer
Question details
The user needs to resolve an issue where a multifunction printer fails to send scan emails via Microsoft 365 using an MX endpoint on port 25.
- Product
- Microsoft 365 / Exchange Online
- Device & OS
- not provided
- Scenario
- Setting up scan-to-email on a multifunction printer using the organization's Microsoft 365 MX endpoint as a relay host.
- Observed behavior
- The printer fails to send emails. The MX hostname resolves to an IP address, but ping requests time out, and the printer reports the hostname is inaccessible despite SMTP AUTH being disabled.
Ensure you have the correct MX record for your Microsoft 365 organization and that you have administrative access to your network's firewall and DNS settings.
Verify Network Configuration and Port 25 Access
Direct send to Microsoft 365 requires outbound access on port 25. Network blockages are the most common cause of SMTP failures when using an MX endpoint.
When bypassing SMTP AUTH to relay messages directly to your Microsoft 365 MX endpoint, the connection relies heavily on standard network configurations. Firewalls and ISPs frequently block port 25 by default to prevent spam, which will instantly cause scan-to-email failures.
Log into your network firewall or router administration panel and ensure outbound traffic on port 25 is explicitly allowed for the printer's local IP address.
Contact your Internet Service Provider to confirm they are not blocking outbound port 25 traffic on your connection.
Use a computer connected to the same network as the printer to run a Telnet or PowerShell test (e.g., Test-NetConnection -ComputerName yourdomain-com.mail.protection.outlook.com -Port 25) to verify the port is reachable.
Configure Exchange Online Connectors and DNS
Ensure your Microsoft 365 environment is properly configured to accept unauthenticated messages from your printer's public IP address.
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Frequently Asked Questions
Why does pinging the Microsoft 365 MX record time out?
Microsoft 365 servers often block ICMP traffic (ping requests) for security purposes. Therefore, a ping timeout is expected behavior and does not prove that SMTP communication on port 25 is failing.
Do I need SMTP AUTH for a printer using direct send?
No. If your printer relies on Direct Send (relaying emails directly to the Microsoft 365 MX endpoint on port 25), SMTP AUTH is not required and can remain disabled for the scanning mailbox.
Why are scan-to-email messages being marked as spam or rejected?
If emails from your printer are marked as spam when using Direct Send, it is likely because your network's public IP address has not been added to your domain's SPF record. Updating the SPF record helps Microsoft 365 verify that your IP is an authorized sender.
