Discovered while testing MDLQA-17698

After setting up all the Outgoing and Incoming mail settings, there is a step where we go to Site admin->Message handlers->Email to Private files (edit).

With 'Validate sender address' disabled I am still getting a validation error when the student attempts to send a file from their email client to their Moodle private files email address.

After replying to the email in my email client, and running cron again, the email gets through to private files, but the 'Validate sender address' setting seems to be ignored when it is set to 'disabled'.