Mine is 4.1.2
Aquamail 1.6.1.0-dev4.4-filter-1 (the sweet spot version for me!)
And just in case, explicitly:
The volume hard-buttons are enabled. They work in the message view, message list view, account view (the font size settings in those three views are independent from each other.)
In the compose view the buttons do not work. But it is indeed possible to change the font size in that view via the menu as in Paris Geek's screenshot above.
Kostya:
1. Is it hard to fix this bug (with the volume buttons) for 4.x?
2. I can understand why in principle someone may want different font sizes in the message view and in the account/message list views. But it seems to me that reading and composing would have similar would have similar requirements for the font size. It's just a bit strange; my naive reaction: I've already adjusted font in one place, why do I need to do that on every screen separately?
In any case, this is not a big deal.