To send email from a GMail or GSuite email address, Google requires your account to be protected by Two Factor Authentication (2FA). In addition to requiring 2FA, you are also required to use an App Specific password when entering your information into Moxie. The combination of these two security pre-requisites ensures that your email account stays secure and you are not required to share your actual password with any third parties (including us!).
If you are using any other email provider, please check out this help article for information on other providers settings (Yahoo, Microsoft, Apple, etc)
If you don't have 2FA enabled on your Google account, you can follow this tutorial for enabling this very important additional security option.
Now that you have 2FA authentication enabled, this tutorial will walk you through generating an "App Specific Password" and setting up your custom email settings for Google.