PHP, Ajax and MySQL

This is for Internal Website (work to be done via Zoom/WebEx/Google Meet). I need to do this using Ajax method. I have a simple PHP site using MySQL in the backend that display a list of servers. Fiddling with the code, I was able to create a button on the site. The whole idea for that button is to when I select on the screen let's say multiple items from the list and click on that button (attached picture), it will read the email value for each row, and send one email containing all the recipients, with pre-defined text (from/subject/body). If any of the email values does not contain "@" the email is invalid, and it's ignored (it could be, that the email field is blank in the DB). I would also want to have an option in the code to be able to specify the destination email address, instead of reading from the MySQL DB email field value.