OK, that's a little vague. Why is it fine to queue up thousands of glyphs that will automatically price themselves, but not fine to leave an addon running all night that will automatically buy all items below a certain threshold? It seems that the line has been drawn firmly around the number of batches that get done automatically. Very complex batches that take a huge amount of time to finish and automatically decide how many items and what price to post them at are OK, even if it feels like they're doing too much thinking for us. What's clearly not allowed is anything that will initiate batches on a regular basis. So having QA3 automatically fire itself up and do a scan/re-undercut cycle every 20 minutes while you watch a movie without pressing a button is not OK.
Think of it this way: A long time ago, in-game macros were much more sophisticated and programmable than they are now. They could, for example, use abilities based on certain conditions. Why did they get stripped down to their current state? If you can write a program to play the game better than a player, then the only people who would play the game would be programmers or people who could afford to hire them. The decision was made to force people to actually play their characters in combat, no longer relying on an I.W.I.N. button.
Economically, this same thing has happened. When Auctioneer had to get rid of Bottom Feeder, we got a valuable data point in trying to determine what Blizzard considers "too much automation". Bottom Feeder was an addon that would cycle through the AH and automatically purchase things based on lists and price thresholds you gave it -- basically, like the snatch list without needing a scan.
This stuff happens in the real stock market too. There is a type of company called a high-frequency trader. High-frequency traders are allowed to program anything they want into their computers until the stock exchange creates a "one trade per hardware event" rule, so now they've started a creepy arms race to get the most powerful computers as close as possible to the stock market computers and do extremely strange things with money too fast for a human to possibly keep up. They aren't completely invisible to us, though.
Selling still feels easier than buying
On my short list of tasks I'd like to automate is buying. Buying and selling both have the same levels of allowed automation, but buying is not asynchronous. What does that mean? You can list something for sale every two days and make sales, but buying requires you to log in for each purchase. I've complained about this before (asking for a system where we could post want-to-buys, or open orders), and I've written about the best way we can automate buying with something like the snatch list. Unfortunately, this has led to situations where the people who win the buying war are the ones who either bought the mobile AH application or have the time to log in the most often. You can try to compete with them by going around the AH to get farmers, but that's still not going to get you to the place these AH campers can go.
My best advice, Pat, is to stick with the batch tools we already have. They're the only way to play fair and the best bet for avoiding getting caught in a botter ban-wave.
As for your mail
I assume you're already using QA3 and something like Postal. It's possible to set QA3 up to automatically mail certain items to certain characters, which is amazingly helpful when you do all your buying on a single character. Postal can be configured to automatically open all the mail in your inbox; however, your inbox is limited to 50 messages at a time, refreshed once per minute. It's a server limitation, and you even see it on the mobile AH.
My method for dealing with large quantities of mail is twofold: I always start off with the mobile AH because you can simply "collect all" gold. This alone makes the monthly cost for the application worth it, in my experience. Once I have only items (unsold auctions, etc.) left in my mail, I log in for real and use postal to pull them out 50 at a time. You can type /console reloadui into the chat window, and you will get another 50 mails if you finish pulling them out before the 60-second timer on the next batch expires. I always collect mail in a low-population city (like Exodar), and I've modified the LUA code in postal to open mails faster than the default fastest rate, when lag allows for it. I also have an addon profile saved in Addon Control Panel specifically for mail; it loads nothing but QA3 and postal. Since I don't rely on the data provided by BeanCounter in Auctioneer, I don't lose anything by not letting it count my sales and returned auctions. This saves a bundle of addon memory and mail time, as well.
Maximize your profits with more advice from Gold Capped, plus the author's Call to Auction podcast. Do you have questions about selling, reselling and building your financial empire on the auction house? Basil is now taking questions for a special series, "Ask an auctioneer," at firstname.lastname@example.org.