This allows you to stand in once place and still use both the auctioneer and the mailbox in the TD AH.
This can be used to "bot" auctions by using a simple autoclicker, and is also good for checking for undercuts/reposting auctions for long periods of time.
You need a flying mount to get under the AH, "Interact with target" keybound, as well as a macro to target the auctioneer (/targetexact auctioneer jaxon) to use this.
First you need to get under the AH:
(I don't know how I could explain this part, so here's a video)
. - YouTube
Once you are under, you can also get a toon that can't fly under by having them get in your 2 person mount.
At this point, you want to target the auctioneer and get between them and the mailbox outside the AH. Move towards the Mailbox until you are in range to use it, then jump and tap "s" (or whatever you have bound to move back). You should be floating a little bit above the ground and be able to use the AH and the mailbox. (Note: There is a very specific spot that you have to be standing in to use both at the same time, so it may take a few minutes to get there.)