No matter what emailaddress I try, every registration failed with "Please enter another e-mail address. We were unable to contact your e-mail server and verify that your e-mail address exists. If you continue to have registration problems, please contact us for assistance.".
I changed
Code:
if (!$vbulletin->options['os_email_fsockopen_support']) {
(on line 17) to
Code:
if ($vbulletin->options['os_email_fsockopen_support'] != '1') {
and after that registrations work again.