SMTP Server Requires a Secure Connection

It's a common issue we have faced in sending email.how to solve this check the following steps. 
  • Enter the correct login password.
  • To remove 2-Step Verification.

  • You have to enable login from other timezone / ip for your google account.To do this follow the link  and allow access by clicking the continue button.
          
  • Go to security settings at the following link and enable less secure apps . So that you will be able to login from all apps.


Next Recommended Reading Send Mail using Gmail SMTP in C#