The error 56 occurs because the SMTP password you entered is incorrect. For Yahoo server, you need to enter the new generated app password instead of your email password. Below are the steps to generate app password and use it in LabVIEW.
1. Sign in to the security page of your Yahoo account.
2.Click
Generate and manage app passwords.
3. Enter the browser you use to log in to Yahoo. For example, if you use Microsoft Edge, so enter Microsoft Edge.
Then, click
Generate password.
4. Use the generated password in the program.
5. Enabled TSL and fill in the necessary items for the program.