core 2.0 sample page with register login: mailkit instead sendgrid possible?

Hello guys,

i am using the core 2.0 registration / login / logout sample page. 

https://docs.microsoft.com/en-us/aspnet/identity/overview/features-api/account-confirmation-and-password-recovery-with-aspnet-identity

Now i try to figure out how to replace sendgrid with mailkit or SMTP (as far as i know microsoft recommends Mailkit).

I am not able to make him send anything is causing headache!

has anybody hints or tutorials how to get this working?