One more thing is there anyway to get email notification when someone reply at my comment on forum.
You should get it automatically, if not then check this URL and adjust your preferences:
Check if your username is entered correctly in the url.
About Aqua Mail
I ran aqua mail on a VM and it doesn't look like they are focused on privacy at all, it is a commercial product.
I don't see any reason to use aqua over k9, k9 has more feautres than aqua mail. If you are looking for design over functionality then try k9 material (discontinued). Your wish.