Webform Product module is used to create a Commerce order (payment) for a Webform submission.

It requires using commerce for payment. This module provides payment for a product type where flexibility and/or complexity is needed.

The subject can be quite difficult with all the new safeguards that have been implemented to combat email spam, address spoofing and actions of bad players.  There are three mechanisms (DKIM, SPF & DMARC) for insuring that an email message is legitimate and making them work together can be quite a task.