It should do that for new notifications as it draws from the URL set in your vBulletin Options (Forum URL).
You should also apply a .htaccess redirect to automatically direct HTTP URLs to HTTPS, like so:
Code:
RewriteCond %{HTTPS} off
RewriteCond %{REQUEST_URI} !(mobiquo|forumrunner|401\.shtml)
RewriteRule (.*) https://www.domain.com/$1 [R=301,L,QSA]
Or something similar. Do note that we cannot provide support for these .htaccess rules or offer equivalent rules for NGINX or any other non-Apache compliant web servers.
Fillip