Change record status: 
Introduced in branch: 
3.x
Description: 

The \Drupal\multiple_email\Form\AjaxConfirmFormBase class is no longer used by the module and it is deprecated. It will be removed in the 4.0.x branch.

There is no replacement. The class was already marked internal; no contributed projects should use it.

Impacts: 
Module developers
Site templates, recipes and distribution developers