this error occurred to me when I setup SMTP virtual sever for SharePoint farm. then I tried to trouble shoot email sending using PowerShell and it also return False.
Trouble shooting SharePoint Emails (SMTP server)
This code will return True if success otherwise will be False.
This error occurred me because of connection issues to SMTP server. thus I go to SMTP properties
Then go to Access Tab and click Connection and Relay buttons and make the radio selection to all except to list below.