I get an email every time a user joins
How can I turn this off?

Hi James,

please try so set:
joomla backend > users > user manger, options, and set Notification Mail to Administrators = No

if the issue still exist, could you please tell me what email content looks like?

Regards

please try so set:
joomla backend > users > user manger, options, and set Notification Mail to Administrators = No

Hi James,

that email is by design as notification, you can turn off it by do this customization:
1. edit /components/com_community/controllers/register.php
2. at line 1035, find this code

$message2 = JText::sprintf(
    JText::_('COM_COMMUNITY_SEND_MSG_ADMIN'),
    $row->name,
    $sitename,
    $name,
    $email,
    $username
);

$sendFalse = true;

$mail->sendMail($mailfrom, $fromname, $row->email, $subject, $message2, $sendashtml);

if (!isset($sendFalse)) $mail->sendMail($mailfrom, $fromname, $row->email, $subject, $message2, $sendashtml);
else unset($sendFalse);