Best Way to Send Many Triggered Emails at Once

I’m working on a donation platform that allows users to send emails to their family/friends to request donations. Users add emails/contact names into the site which are stored in a database. Each email I want to have custom messages from the user. I figured that triggered emails are the best way to accomplish this type of customization.

What is the best way to send multiple triggered emails at once to different email addresses, for people who are not necessarily platform users?

My initial attempt was to use wix-crm to create a new contact for each person, store the id in a database, and use the wix-crm.emailContact() method to email each person individually. The problem I encountered was that some emails which it is trying to add, are already Users of the site and cannot be added as contacts. Why is this?

Thank you in advance for your assistance!

You will find the reason why in the Wix API Reference for Wix CRM API and Wix Users API.

What’s the difference between wix-crm and wix-users?
The CRM API contains functionality for working with your site’s contacts. The Users API contains functionality for working with users who are logged-in members. Note that all members are also contacts, but contacts are not necessarily members.

Also, note that if you simply use Wix CRM or Wix Users you will only be able to send emails to the current user or the current logged in site member.

If you are wanting to send emails to contacts who are not viewing your site or site members who are not logged in currently, then you need to be using the backend version of each API.

https://www.wix.com/corvid/reference/wix-crm-backend.html

https://www.wix.com/corvid/reference/wix-users-backend.html

So can I use strictly the Wix CRM Backend API if I am trying to send emails to a list of people that could be just contacts and not necessarily members