Ive been searching a long time for something like this now, here's what i need:
An Addon which counts every incoming gold from my auctions, easily through the mail or something like that, so that i can see how much income i actually have.
Auditor is what you're looking for.
You can also expand the Source (as seen in the screenshot) so it shows you how much gold you've obtained from various sources:
Yeah, I still use Auditor myself, even though it hasn't been updated in 3 years. I wish someone would pick up this addon, I haven't found anything quite like it.