Many do not know what this is all about. If you change the setting you may be open to receiving a lot of spam. Default mail means anything before @yourdomain will be delivered to the mail address you give as the default. This means that any mail that has no mail account will be delivered. For example: junk@yourdomain, anyone@yourdomain , trees@yourdomain etc will be delivered even if no mail account exist or is setup. It is best to have default mail sent to :fail: so it will be bounces back to the sender. Doing this will stop any mail not actually set up by you. Default says.. "I don't care what the name is before the @yourdomain I am going to deliver it."
It is a favorite trick of spammers to get a Domain Name then just put anything in front of it to make it an email.
