Send an Email throws error

I have a new install of CivicSpace 0.8.2 rc3 with CiviCRM 1.1 installed. I've added new users to the system through the administer > users, but anytime i search for those users in CiviCRM, select one, fill out the email form and hit send, I get the following error:

unrecoverable error
Sorry. A non-recoverable error has occurred.

Return to CiviCRM menu.

error

Array
(
[callback] => Array
(
[0] => CRM_Core_Error
[1] => handle
)

[code] =>
[message] => unable to add recipient [cocteau@wact.net]: Invalid response code received from server
[mode] => 16
[debug_info] =>
[type] => pear_error
[user_info] =>
[to_string] => [pear_error: message="unable to add recipient [foo@foo.net]: Invalid response code received from server" code=0 mode=callback callback=CRM_Core_Error::handle prefix="" info=""]

any ideas as to what's wrong?
)