To help others following Spam's question, his original post and screenshots are posted in this thread:
http://www.aqua-mail.com/forum/index.php?topic=5000.0 . Unfortunately, he jumped to this thread to continue.
@Spam:
I see that what you are looking for is essentially a built-in folder-explorer, working similarly to what you find in "Windows Explorer" on Windows, or "Folders" built-in stock app on Android, - but with the ability to open and read e-mail messages right in it.
That is not available in Aquamail.
Furthermore, to the best of my knowledge, in Aquamail, you cannot delete a folder (but you can create one).
So, I see that it would be difficult to implement your workflow in Aquamail (and I suspect in several other mail apps.)
I'd like to point out that your workflow is not very typical. As a matter of fact, it is the first time I hear anything like this, - when a user creates a temporary folder for a message and deletes it. It sounds overly complicated to me. And that type of workflow is definitely not what e-mail app designers usually have in mind.
I cannot speak for the developer, Kostya, if he might decide to implement something like you proposed. (And I can see some advantage of the "dynamic message explorer" even for people who are not using the workflow like yours. It could be helpful when searching for a specific message through a multitude of folders.) But I would guess that it probably wouldn't be his first priority, given the fact that not that many users are interested in that.
In any case, at this point, you wouldn't be able to do that in Aquamail without any changes.
If you wish to make adjustments to your workflow, I can offer you a scenario that will be similar to yours and could be easily implemented in Aquamail (or for that matter in most, if not all mail apps).
What you do with that temporary folder is just marking your message with a distinct property. The same effect can be achieved by marking the message with a "star". Then all your "starred" messages are equivalent to the messages being in its own
silo folder.
And then you can easily delete the message in Aquamail, when your order is completed.
You can also choose "starred first" while viewing the message list in a folder, and that would allow you seeing all your upcoming orders together.
I hope this helps.