(Apologies in advance if this is a re-post, I did my search homework and could not find something specifically matching this.)
So as the title states, I discovered that you can have access to your bodyguards special ability before level 3. For anyone confused as to what I mean by this, if you build the Barracks via the Garrison you can assign certain followers at level 2 with the "Bodyguard" trait to follow you around in the open world, to assist you in combat. Here is a list of the known bodyguards:
Bodyguard - Garrison Ability - World of Warcraft
Each time that you kill a mob out in the world, you gain 10 reputation with your follower. There are various exploits out there to help you in gaining much faster reputation with them, please utilize the search tool to check out the ones that people have contributed! Once your bodyguard reaches the third level of reputation, they unlock unique abilities. The ability that Talonpriest Ishaal unlocks is a mobile mailbox. Now we get to the part of the discovery. First, for a point of reference - here is the current xp value of my Talonpriest Ishaal:
https://i.imgur.com/aGf13E1.png
If you interact with him/her, the normal dialogue is to tell them to return to the Garrison. However, I discovered that if you interact with your Bodyguard while in combat it bypasses the need for you to have them be max level and utilizes their ability that is normally unlocked at level 3. Image below:
https://i.imgur.com/Z8TKOa7.png
Screen shot was cropped to show the important bits: my combat status, my same Talonpriest Bodyguard and my ability to use his mailbox. This may also be used to utilize the level 3 abilities of the following Bodyguards:
Tormmok: personal repairs in the field
Leorajh: personal mission table in the field
Once you have interacted with them while in combat, you can utilize their special ability until you move away from them or end the interaction. This is nice for people who are mailing things off to alts while in the field.
Edit: fixed some basic grammar/sentence issues I found.