The mail tab under Settings displays the following fields:
As you set up an store application to synchronize with your Gmail account, a screen asks for your Gmail SMTP information.
Now you can test it . Go to Marketing > mail and try to send email to your customers.
Create & use App Passwords click the below link
https://support.google.com/accounts/answer/185833?hl=en-GB
https://security.google.com/settings
You can read Microsoft support for more information about app password.
https://support.microsoft.com/en-us/account-billing/using-app-passwords-with-apps-that-don-t-support-two-step-verification-5896ed9b-4263-e681-128a-a6f2979a7944