I have set up an event with webform/civievent and the registration confirmation & receipt is not sending to anonymous sign-ups. While logged in and signing up it will email me (if I am the sign-up), but for anonymous users it won't. I have the send receipt box ticked off in both the contribution page and the event itself. The payment is going through and the participant is being registered correctly, the receipt will just not auto-send. I am using Drupal 7, CiviCRM 5.3.1, and webform version 7.x-4.17.
Ah - ok - this is what's happening:
- if the event is FREE -> then no receipt is issued via CiviCRM workflow message templates
- if the event is FREE && if participants make a donation -> then the participants get an email message from the CiviCRM workflow message template - contribution online
So your workaround is a good one - a simple Email message that is triggered via CiviRules (add Participant to a certain event) - or you could even do a simple Email message from Webform -> Emails.