Mail Delivery System <MAILER-DAEMON[a]gproxy1.mail.unifiedlayer.com>

I have a list of 50,000 emails. Some of them are non-existent. When we send email to that list, some emails are not being delivered (given that some recipients are non-existing), so we get an email like this: Mail Delivery System <MAILER-DAEMON@[login to view URL]> I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below.... We need to attach these notification emails to a php script to flag these emails in the database so we don't use them in future time. Thank you.