1. Go to evenium.com 
2. Click My Events 
3. Click on the name of the event under the I organize section
4. Click Configuration on the purple bar 
5. Click Invitations & Emails 
6. Click See all emails sent
7. Click on the Errors column header
8. If you have a sent email that has errors associated to it, click on the name of the email under the Message title column
9. Filter the Status column on the Error value.