Change record status: 
Project: 
Introduced in branch: 
12.0.x
Introduced in version: 
12.0.0
Description: 

When sending transactional mail it is required to set an appropriate From address. This address is taken from system.site:mail configuration value. That config value has been a required value for new installs since Drupal 8.

Nevertheless, a fallback to the sendmail_from ini setting was present in various places throughout core (e.g., in MailManager). This fallback has been removed.

Impacts: 
Module developers