"99 % of failed (bounced) emails have a wrong recipient address. Your sender email address set in Qondor receives an email notification if an email message cannot be received because the address is wrong.
For example, if I send an offer to a customer or a message to a participant from email@example.com to an email address that doesn't exist, I as the sender will receive an email from Qondor with subject "Bounced + subject of the failed email", stating why the email failed. If a booker registers on a form with an email address that doesn't exist, the sender address will also receive a notification.
Please note that we can only report on messages that we know cannot be received. You will not be notified of messages ending up in a spam, junk or clutter.
Hope this will help you follow up where needed!
P.S.: If you want more information about the various types of bounced email, we recommend this article from MailChimp.