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Sends a welcome email to new users after they have activated their account, it includes their username and password in the email for confirmation purposes. It also provides a link to their newly registered blog.
<?php wpmu_welcome_notification($blog_id, $user_id, $password, $title, $meta); ?>
wpmu_activate_signup calls this function to send the welcome email to the user, the parent function handles the activation of the end users account.
wpmu_welcome_user_notification does the same thing except that it is for who only registered for an account and did not register for a blog.