By default Magento only has one filed to input the recipient of the contact form (in admin).
If you would like to get this sent to several email addresses then a small hack is required as Magento adds some encding to address in this field.
firstname.lastname@example.org>, name <email@example.com
to send to two recipients. name is the name shown as the address in the second mail.
To send to 3 addresses use
firstname.lastname@example.org>, name <email@example.com>,name2<firstname.lastname@example.org
To sent to 4 or more, just add more as in the 3 addresses example