Right e-mail: email@example.com
Wrong e-mail: firstname.lastname@example.org
No, you can't save it in a separate mailbox. However, you can hold it in your mail.box, instead of returning to the sender by modifying the configuration document. Go to the Router/SMTP tab then select the Advanced tab, then Controls. The field "Hold undeliverable mail" should be enabled. Once enabled, restart the router and you are all set.