How to Set Up an Office 365 SMTP Relay Connector for Printers, Scanners, and Business Apps

There are three main relay methods in Microsoft 365:

1. SMTP Client Submission (Preferred if possible)

• Uses port 587 with TLS and authentication (username + password).
• Works best for apps/devices that support modern authentication.
• Each device must be configured with a licensed mailbox account.
• Settings:
  • SMTP server: smtp.office365.com
  • Port: 587
  • Encryption: TLS
  • Username: mailbox email address (e.g. scanner@yourdomain.com)
  • Password: mailbox password / app password (if MFA enabled).

2. Direct Send

• Sends mail directly to Office 365 without authentication.
• Only works when sending to internal recipients (inside your domain).
• Useful for devices that cannot authenticate.
• Requirements:
  • Device must be on your public IP that’s allowed in Exchange Online.
  • Use your Microsoft 365 MX endpoint as the SMTP server (e.g. yourdomain-com.mail.protection.outlook.com).
  • Port: 25
  • TLS: optional, but recommended.

3. Office 365 SMTP Relay (Connector-based)

• More flexible: allows sending to internal and external recipients.
• You create a mail flow connector in Exchange Online that authorises by public IP address.
• Steps:
  1. Log into Microsoft 365 Admin Center → Exchange Admin Center.
  2. Go to Mail flow → Connectors → Add new.
  3. Choose:
     • From: Your organisation’s email server
     • To: Office 365
  4. Give it a name (e.g. “Office devices relay”).
  5. Specify the public IPs of your devices/apps that will send mail.
  6. Save connector.
  7. Configure devices/apps with:
     • SMTP server: yourdomain-com.mail.protection.outlook.com
     • Port: 25
     • No authentication needed.
     • TLS if supported.

✅ Which option should you choose?

• If device supports authentication → use SMTP client submission.
• If only internal mail → direct send.
• If external mail needed & no authentication support → connector-based relay.