Unable to register at elmer forum

[RexLinz]

I tried to register at elmer forum to report an issue, but after entering my information I got the following error

Fatal error: Uncaught Error: Call to undefined function mail() in /home/np29546/public_html/forum/includes/functions_messenger.php:1985 Stack trace: #0 /home/np29546/public_html/forum/includes/functions_messenger.php(637): phpbb_mail('=?US-ASCII?Q?RE...', 'Account passwor...', 'Hello RExler\n\nY...', 'From: "=?US-ASC...', '\r\n', '') #1 /home/np29546/public_html/forum/includes/functions_messenger.php(400): messenger->msg_email() #2 /home/np29546/public_html/forum/phpbb/ucp/controller/reset_password.php(275): messenger->send('0') #3 /home/np29546/public_html/forum/vendor/symfony/http-kernel/HttpKernel.php(151): phpbb\ucp\controller\reset_password->request() #4 /home/np29546/public_html/forum/vendor/symfony/http-kernel/HttpKernel.php(68): Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object(phpbb\symfony_request), 1) #5 /home/np29546/public_html/forum/app.php(35): Symfony\Component\HttpKernel\HttpKernel->handle(Object(phpbb\symfony_request)) #6 {main} thrown in /home/np29546/public_html/forum/includes/functions_messenger.php on line 1985

Looks like the website trying to create an email to confirm registration but failing.

Strange thing: Afterwards I have been able to create a new thread (showing my name in the top right), but trying to submit it I have been redirected to the registration page again. Trying to log in again I get the error "You have specified an incorrect username. Please check your username and try again", trying to reset the password I get the same error as shown above.

Such I try to get started and report this error first here in hope someone could fix that. Thanks!