Changes

This option would involve having to use the user credentials, a very bad idea in general, because it would involve either our server even temporarily storing user credentials as a responsibility, or providing a third party server with the user credentials, an uncontrollable risk.  

This option would involve having to use the user credentials, a very bad idea in general, because it would involve either our server even temporarily storing user credentials as a responsibility, or providing a third party server with the user credentials, an uncontrollable risk.  

* Using email provider APIs like Gmail API [ https://developers.google.com/gmail/api/quickstart/js ]

* Using email provider APIs like Gmail API [ https://developers.google.com/gmail/api/quickstart/js ], or free tiers of something like MailChimp or PostMark.