With the right followers, it’s possible to get yourself a piece of genuine Highmaul raid loot without ever setting foot inside the raid. Before you endeavor to do this, you should know that the Dwarven Bunker/War Mill and Salvage Yard are basically required to do this in any sane amount of time. You need both buildings to get enough follower armor and weapon upgrades, as these missions require a roster of ilvl 645+ followers to complete.
Your first raid mission will unlock when you have 3 followers at 645 or higher item level.
The mission should stick around for at least a couple days if you want to spend some time getting other followers ready.
After completing a raid mission, your next one will unlock 2 weeks later.
Any piece of loot from the raid appropriate to your loot specialization can drop, with the exception of weapons. Just like normal drops, these can be warforged, socketed, or have tertiary stats.
The quality of loot is based on your current progression in the raid itself:
Normal caches (ilvl 655 loot) are rewarded if you’ve killed 0-14 bosses in normal mode.
Heroic caches (ilvl 670 loot) are rewarded if you’ve killed 15+ bosses in normal mode.
Mythic caches (ilvl 685 loot) are rewarded if you’ve killed 15+ bosses in heroic mode.
Mythic caches plus a bonus of 1000 gold are rewarded if you’ve killed 15+ bosses in mythic mode.