Error when sending mail to contacts

When sending mail to contacts, I receive the following error:

Error Details:

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

[code] => 111
[message] => Connection refused
[mode] => 16
[debug_info] =>
[type] => PEAR_Error
[user_info] =>
[to_string] => [pear_error: message="Connection refused" code=111 mode=callback callback=CRM_Core_Error::handle prefix="" info=""]
)

However, despite the error, the mail actually DOES successfully send out. CiviCRM 1.7 beta 9184 (drupal/php5)