If an email you send to a customer is not delivered/ bounces back, you should receive a notification at the email address you use for your Gingr user account. If you find that you are not receiving these notifications, you may want to check the settings on your email provider's website, to make sure that bounced email notifications are enabled.
You can also check the Outgoing Email Log for an email's status at any time.
Note: Gingr helps avoid bounced emails by helping to prevent typos when entering a customer email addresses. On both the New Customer Registration and New Owner pages, Gingr validates the email address entered, and even provides suggestions. For example, if you enter firstname.lastname@example.org, you (and customers) will receive a message like this: