Creating user documentation for software is a challenging task. True, you cannot provide an answer for every use case, and sometimes the author of the app is too close and familiar with "everyday tasks" to create a truly user-focussed document, without assumptions that are, for him, 'wired in'. In some respects the task is just as daunting as writing the software and sometimes a great deal less fun.
On top of this, phone apps tend to have rather slim documentation, compared with desktops, but aquamail is heading into the space between these, so needs some how-to documentation for a few things, but 'just works' for most tasks.
However, some of the best "user documentation" I have used has been (in a way) crowd-sourced. I frequently find myself asking "using blahblah software, how do I do x".
For open source projects, particularly, multiple authors have solved a problem, in a format that poses a question, or set of related questions, and then provides step by step answers.
Although AM is not open source, I don't see why the same approach could not apply.
It would ideally need a framework - a wiki or something, ideally, to hang it all together, but for now, the "how do I..." part of this forum is not a bad place to start.
The difference is: At present most threads there kick off with a question, that may or may not get answered. It needs more answers from users, I think.
Why not, if someone knows how to do something that hadn't been written up before (because you know how, and never had to ask), write it up and post it there? There are some 'tutorial' items there already. It just needs a few more, from the users that have quietly mastered everything, for the benefit if the rest of us (who still need a little help).
Not sure if it would be possible to make some of these 'sticky', the better to find them.
Just my 2pence worth, and kostya may disagree, as is his right of course!