Send .NET App Email via Gmail

Error:

The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.0 Must issue a STARTTLS command first.

Fix:

Step (1): smtp.EnableSsl = true;

if not enough:

Step (2): “Access for less secure apps” must be enabled for the Gmail account used by the NetworkCredential using google’s settings page: