Non-recoverable error upon send e-mail to contact without name data

I think this error only occurs when trying to send to contacts in CRM who have an e-mail address listed but no first or last name. However, I could be wrong. It is also possible that the error is somehow caused by people who have CRM listings just because they are Drupal users. Not able to determine.

The error goes away if I edit the user in question and add a first and last name.

Anyway, this is the error that comes up when trying to send an e-mail through the actions list to contacts with no name:

Sorry. A non-recoverable error has occurred.

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error

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

[code] =>
[message] => unable to add recipient [kbearman@isd.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 [kbearman@isd.net]: Invalid response code received from server" code=0 mode=callback callback=CRM_Core_Error::handle prefix="" info=""]
)