recurring contribution receipt comes from logged in user

When a recurring contribution is triggered, the receipt is sent from the currently logged in user.

In the wild, this has been documented when using the iATS extension, which is triggered to send recurring contributions receipts by a cron job, which is typically run (in Drupal at least) as the UID 1 - which corresponds to a CiviCRM contact. Often, this CiviCRM contact is not the person you want sending a receipt.

I'm not sure exactly what happens if a recurring contribution receipt is triggered via IPN, which case it may be anonymous.

See: https://github.com/iATSPayments/com.iatspayments.civicrm/issues/170