vBulletin attachments are served through php for two reasons:
1. Attachments can be stored in the file system or in database.
2. Attachments access can be limited based on user group and even section based settings i.e. attachments uploaded in threads under LiteSpeed Cache can only be visible to usergroups who have access to this section, while others will get denied message.
Since this is how vBulletin behaves out of the box, I doubt we can use x-sendfile.
With respect to using Litespeed cache, will the default vB plugin you guys have, store these attachment requests individually as well?
Asking because the images aren’t just being served in particular threads, they are embedded in other websites as well and that is what is really causing the load.
Also does that plugin works with vbulletin 4.2.1 and vbseo 3.6.1?