Fix Microsoft 365 SMTP Authentication Errors on an Epson WF-3720
Question details
The user needs to resolve an SMTP authentication error when sending scanned documents from an Epson WF-3720 through Microsoft 365.
- Product
- Epson WF-3720 and Microsoft 365 Exchange Online
- Device & OS
- not provided
- Scenario
- A printer or its associated scanning software is configured to send scanned documents by email through Microsoft 365.
- Observed behavior
- The scan-to-email workflow reports an SMTP authentication error. Possible causes include incorrect credentials, mailbox restrictions, incompatible authentication settings, or outdated TLS support.
Record the exact error message and identify whether the SMTP settings are in the printer or its scanning software. Have a Microsoft 365 administrator confirm whether the workflow uses authenticated SMTP client submission or connector-based SMTP relay.
Check mailbox access and authenticated SMTP submission settings
Use this approach when the scanning workflow connects to Microsoft 365 using a mailbox account.
Sign in to Outlook on the web with the account configured for scanning and send a test email. If sign-in or sending fails, ask your administrator to check the account, Exchange Online mailbox, and any sending restrictions before changing the printer settings.
Open the scan-to-email SMTP settings in the printer configuration interface or scanning software. For Microsoft 365 client submission, check that the server is smtp.office365.com, the port is 587, STARTTLS is enabled, and the username is the full mailbox email address. Use the mailbox address as the sender unless another address has been granted Send As permission.
Ask your administrator to open the Microsoft 365 admin center, select Users > Active users, select the sending account, and check Mail > Manage email apps for Authenticated SMTP where available. The administrator must also check organization-level restrictions and whether the device supports an authentication method permitted by Microsoft 365. A successful browser sign-in does not prove that password-based SMTP authentication is allowed.
Use Epson Software Updater or the firmware update option available for the printer to install current firmware. Check Epson's documentation for TLS 1.2 or later and, where required, OAuth support. Do not rely on TLS 1.0 or TLS 1.1 for Exchange Online SMTP connections.
Save the SMTP settings and send a small test scan to your own mailbox. If it fails, copy the complete error code and message and ask your administrator to review the sending account's authentication settings and restrictions.
Configure Microsoft 365 SMTP relay for a compatible scanning workflow
Use connector-based relay when the device cannot use a permitted mailbox authentication method and your network meets Microsoft 365 relay requirements.
Use WPS Office to work with documents alongside your scanning workflow
WPS Office does not fix Microsoft 365 SMTP authentication or configure printer email delivery. It offers a free, lightweight, easy-to-use Office alternative with a familiar interface and Microsoft Office format compatibility, making it easy to migrate document work while your administrator resolves scan-to-email delivery.
Frequently Asked Questions
Why does the printer reject my credentials when Outlook on the web accepts them?
Browser sign-in and SMTP authentication use different access paths. Microsoft 365 may block password-based SMTP even when web sign-in works. Ask your administrator to check the mailbox's Authenticated SMTP setting, organization policies, and the authentication methods supported by your printer or scanning software.
What does “Client was not authenticated” mean?
Microsoft 365 did not accept the connection as authenticated. Open the scanning workflow's SMTP settings and check the full mailbox username, server, port, STARTTLS setting, and supported authentication method. If you intended to use relay instead, have your administrator verify the Exchange Online connector rather than adding mailbox credentials.
Is TLS 1.0 sufficient for Microsoft 365 scan-to-email?
No. Use a device or scanning application that supports TLS 1.2 or later for current Exchange Online SMTP connections. Check Epson's firmware updates and technical documentation; an older recommendation to use TLS 1.0 or later is not sufficient.
Can I use SMTP relay if the printer cannot store a password?
Potentially, but your organization must meet the relay requirements. An administrator must configure Mail flow > Connectors in the Exchange admin center and establish supported identification through a static public IP address or certificate. Your network must also allow outbound port 25.
How can I email a scan while SMTP delivery is being fixed?
Use an available scan-to-computer or save-to-file option in the Epson scanning software. Save the scan locally, open Outlook on the web, create a new message, and attach the file. This bypasses the printer's SMTP connection without changing Microsoft 365 security settings.
