AquaMail lets you move messages into the server side spam folder.
To set up / check:
Long press the account -> options and folders -> folders.
Find the server side spam folder (for Gmail, it's "Spam" or "Junk" below "[Gmail]"), tap it, choose Sync as spam (or Spam, don't sync).
Now you will have "move to spam" menu items in message list (after selecting one or more messages) and in message view.
And hopefully, the mail server's spam filter will *learn* and adjust its filtering rules as you move messages there.