Re: I don't think Aquamail creates any folder on the server automatically. It must've been created by another app, and Aquamail found it before "Trash" folder.
Correct. Aqua Mail never creates those "special" folders (Deleted / Sent / Drafts / Spam / Archive), but it detects them.
Re: Take a look at the FAQ.
Sure, and to actually "remap" the app's Deleted folder (to the right server folder), please:
- Long press on the account
- Options and folders
- Folders
- Let it refresh (10-20 seconds)
- Find the right server side Deleted folder ("Deleted Messages", "Deleted Items", "Bin", etc.)
- Tap its name
- Choose "Sync with Deleted" from the popup.