Thanks for your reply.
To reiterate: My Settings menu includes the following choices for deleting messages, which differ somewhat from the FAQ:
Delete (the account's delete option)
Move to Deleted
Delete permanently
Hide (keep on server)
Whereas the FAQ addresses these three choices:
Move to Deleted folder first
Delete from the server immediately
Hide in the app, keep on the server
The two 'hide' choices are identical, obviously.
"Move to Deleted" is probably the same as "Move to Deleted folder first."
"Delete permanently" is probably the same as "Delete from the server immediately."
That leaves "Delete (the account's delete option)" which is nowhere explained in the FAQ.
I have reproduced the contents in its entirety. If you see the phrase "Delete (the account's delete option)" in the text below, you have better eyes than I.
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There are three methods to delete messages.
The choices are: “Move to Deleted folder first” / “Delete from the server immediately” / “Hide in the app, keep on the server”. The initial default setting is “Move to Deleted”.
When using IMAP, you can synchronize the [ Deleted ] folder with the server if you like. With EWS, this is always the case.
Deleting messages from Gmail requires that they first be moved into the Deleted folder, which in turn has to be set up to synchronize with “[Gmail]/Trash”. When setting up a Gmail account, AquaMail sets this up automatically.
For POP3, the Deleted folder is local, so don’t forget to empty it from time to time (this will delete messages from the server).
The default delete method is specified under “Options and folders” / “Account options” separately for each account (long press on the account in the main screen to open). The setting is called “Deleting messages”.
Changing the default changes the icon you see when viewing a message or when selecting several messages in a message list.
You can apply a non-default delete method in a message list by using the menu (or the “three dots” button which Google calls “overflow”).
So for example, you can keep the default method as “Move to deleted”, and if you see spam messages you’d like to delete immediately, select them, then use the Menu / Overflow button and choose “Delete now”.