You can get the Spam folder to show in your list of folders, the same as with any other folder you have, but only for IMAP accounts I think. Long press your account and then choose Options and Folders and then Folders. You can then set up the spam folder to sync with the spam folder in your email account. I have not tried it but I guess that you can then drag and drop to the Spam folder, in which case it will sync with your email account. I do not know if Aquamail has any spam learning features, but I would be surprised if it did.