You are not talking about *long* messages, but *too-long-to-be-handled-on-a-device-screen* messages. AquaMail is an email app after all.

Paris Geek:
I hope that was a "tongue-in-cheek" comment.

(Otherwise, it would be joining the company of suggestions on how users should do things with their devices from MSFT and ADBE, in /dev/null.

)
Aquamail is perfectly suitable for what I am using it.
Here are a few use cases for the situation described:
1. Checking the summary at the bottom of a long message that contains automated script output from a server is a simple task that can be done on a phone. Depending on the day and events, those messages can range from 1 to almost 200 kB.
2. Finding information in the signature (e.g. for the phone number) at the bottom of a long chain of e-mail exchange is yet another simple function for which Aquamail and a smartphone are very suitable.
3. Occasionally, someone forwards a message with either the "To:" header with a long list of original recipients (some 100-200 people) and only a short message, or with a long chain of forwards, where some 22 forwarding headers are at the top of the message of the body.
In all those cases, ability to quickly jump to the bottom (and occasionally to the middle) of the message is convenient. Desktop mail applications have the button "End", and window-based programs typically have a scrollbar.
Now, whether Kostya considers this important enough (and easy enough) for him to correct/implement, - I'd leave it to him to decide. Seeing that he has a scroll-knob implemented in the list of messages, I am guessing that it would be relatively simple, but I might be totally wrong.