We have configured Odoo Outgoing Mail and it works fine.

But today our Mail Provider had some problems and the outgoing mails (Invoice per Mail) from odoo could not be sent. A "Undelivered Mail Returned to Sender" message was sent from Mail provider back to the catchall email address. Odoo has processed this mail (because it is set as readed) but the message is nowhere shown. 

Any hints on how to handling error mails returned from mail provider would be great because of there is a big risk when mails are not sent, but in odoo they are shown as successful sent!