1) Buy a domain, doesn't matter what name or extension ( i like to use mail in the name but whatever)
2) Add it to your hosting, make sure your host supports catchalls, not every hosting (especially cheap shared hosting) supports that
3) Now go into your Cpanel, look in the mail section for: "Set Default Address" then select "Forward to Email Address" and fill in any email that you wanna receive the mails on
Now you have a catchall, every time you create a mail for that domain it will be sent to the email address you have put in that text box..
Hope this helps you