It's really easy to select failed emails (emails that could not be sent) in Mass Mailing News. From the taskbar, go to the “Contacts” menu and click on “Other selections”, then select “Select failed”. The email addresses will be selected and you could edit and/or delete these contacts.
Note: To have access to all the options from the “Contacts” menu, first, you need to click on the “Contacts list” tab. This way, choices will be activated.