Send a conditional email notification when a custom field value changes in Post Type

There’s no way to do this without a bit of programming. You need to look at these pieces:

  • A WordPress hook like save_post lets you do something when a post is saved or updated
  • wp_mail is how you send an email
  • get_field is how you look at the value of an ACF field.

You’d need to write some code to put them together how you want to, but the details of doing that are beyond the scope of this stack and you’d need to learn some coding, how to run code in WordPress through a plugin or functions.php