How to send the built-in email from custom authentication function?

I am using the Email/Password Authentication Provider.

For specific reasons I have to use the “Run a Confirmation Function” for the User Confirmation and also “Run a Password Reset Function” for Password Resets.

I don’t have any 3rd party email service like Amazon SES, so how can I call the Mongodb Backend from my functions to send the user confirmation/password reset email to a specific email? Is there a simple API call to make this happen? It should be possible because if you select “Send a confirmation email” then it just sends the mail from MongoDB backend too.