And let's not forget:
AquaMail settings -> Send notifications.
These are app-level settings that will be used for an account (any account) unless there is a per-account override.
And to check if there is a per-account override for a specific account:
Long press an account -> Special settings.
There is a checkbox for several different types of things you can override on a per-account basis. If unsure, switch all those checkboxes off.