Forum Problem after user Registration
 

I'm new to vbulletin, and I am having this message show up after a user registers on the top of their screen. Can anyone help?

Warning: fsockopen() [function.fsockopen]: php_network_getaddresses: getaddrinfo failed: Name or service not known in [path]/includes/class_mail.php on line 637

Warning: fsockopen() [function.fsockopen]: unable to connect to tcp://:25 (php_network_getaddresses: getaddrinfo failed: Name or service not known) in [path]/includes/class_mail.php on line 637

Warning: Cannot modify header information - headers already sent by (output started at [path]/includes/class_core.php:4372) in [path]/includes/functions.php on line 4599