Client not authenticated to send mail office 365

The classic "Client not authenticated to send mail" error!

This error typically occurs when the client (e.g., an application or a device) is trying to send an email using Office 365, but it's not properly authenticated to do so. Here are some common causes and solutions:

Cause 1: Missing or incorrect credentials

• Make sure you have the correct Office 365 credentials (username and password) and that they are entered correctly in the client application.
• If you're using a service account, ensure that the credentials are valid and not expired.

Cause 2: Authentication issues with Office 365

• Check if the Office 365 account is set up correctly in the client application. Ensure that the account is configured to use the correct authentication method (e.g., OAuth, Basic Auth, or NTLM).
• If you're using OAuth, ensure that the client has been granted the necessary permissions to send emails.

Cause 3: Firewall or proxy issues

• Check if there are any firewall or proxy settings blocking the client from connecting to Office 365.
• Ensure that the client is configured to use the correct proxy settings or firewall rules.

Cause 4: Office 365 account settings

• Check if the Office 365 account is set up to allow less secure apps to access the account. If not, you may need to update the account settings to allow less secure apps.
• Ensure that the Office 365 account is not set up to use two-factor authentication (2FA), as this can cause authentication issues.

Cause 5: Client configuration issues

• Check the client application's configuration settings to ensure that they are correct and up-to-date.
• Ensure that the client is configured to use the correct Office 365 endpoint (e.g., outlook.office365.com).

Troubleshooting steps

1. Check the Office 365 account settings and ensure that the account is set up correctly.
2. Verify the client application's configuration settings and ensure that they are correct and up-to-date.
3. Check the firewall and proxy settings to ensure that they are not blocking the client from connecting to Office 365.
4. Try sending an email using a different client or application to isolate the issue.
5. If none of the above steps resolve the issue, contact Office 365 support for further assistance.

I hope this helps you resolve the "Client not authenticated to send mail" error!