It's really easy to select bad emails in Mass Mailing News. From the taskbar, go to the “Contacts” menu and click on “Other selections”, then select “Select bad emails”. The email addresses will be selected and you could edit and/or delete these contacts.
Note: To have access to all the selections from the “Contacts” menu, you first need to click on the “Contacts list” tab. Then, the options will be activated.