$from parameter is not set

According to the module description, it should be possible to set the sending email address with the $from parameter

simple_mail_send($from, $to, $subject, $body);

However, this does not appear to work. After taking a look at the code, it appears that MailManager is being used to send the mail. This does not accept a $from parameter, but rather has a $reply paramter that sets the Reply-To header. This means that all mail send with simple_mail is sent from the system.site email address.

https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Mail%21Ma...

MailManager is a replacement for drupal_mail, which did accept a $from parameter.

https://api.drupal.org/api/drupal/includes%21mail.inc/function/drupal_ma...

My suspicion is that when this module was upgraded from the Drupal 7 version this difference was missed.