Gmail is a GREAT tech support tool.
I've been selling downloadable games on my website since 2007. And in those years I've had plenty (and by plenty I mean hundreds) of emails to email@example.com from people who need help. 99% of the emails fall into two categories:
1. (<7 days from purchasing) I am having trouble downloading/unlocking/installing
2. (>7 days from purchasing) I bought a game quite some time ago and I switched computer/email/gender/whatever and I lost my original download instructions.
When I first built my little order/download system, I made sure to stuff every transaction I made into a MySQL table. I kept transaction numbers and emails and products purchased and all that stuff. And that way if anybody from category (2) above had a problem, I could look up their order.
And I have NEVER used that table.
It's still out there, full of everything I'd need to look up an order. But I don't use it because I have Gmail. When someone buys a game, the last step on my side is a little piece of PHP generates and sends and email to the them with instructions on how to download and install the game. And, just to be safe, I also sent that email to firstname.lastname@example.org where it is quietly filtered and stuffed it into a Gmail folder.
And that's pretty-much my tech support. If anyone emails me saying "My name is Fredrick Fribble and I bought Bulldozer around two years ago", I can find their order by searching my gmail. Re-sending their download instructions is as easy as re-forwarding that old email back to them. There have been a couple of occasions where I had to go back and forth a couple of times because they ordered under a different name or changed email addresses or something, but I have always been able to find their order and send it back to 'em. Usually in a couple of minutes.
So I guess the suggestion here is not to overengineer things. I realize this wouldn't scale if your orders got into the huge numbers. But my orders do number in the thousands, and this little system is showing no signs of breaking down.