@sthalik:
I understand your frustration: you discovered and reported the behavior that deviates from the standards and/or common logic, but it is not labeled as a bug.
(Been there, done that, and not only with Aquamail or other software, but with other ("everyday") things in life.)
But I don't think Kostya's response is rude or nonsense. It might not be the most pampering response (as prescribed e.g. by Dale Carnegie), but the way I read his response is: "Yes, that's deliberate, to compensate for the real-life situations [even if those violate RFCs], and sorry but I have reasons why I am going to keep it that way." It's like the [in]famous "It's not a bug, it's a feature".
If this "feature" were affecting me, most likely I'd be reporting it as you did. And I would be frustrated in a similar way.
But at the same time, I see why Kostya made his decision for this feature. There is a much larger portion of any [general purpose] software users who are ignorant about the standards or what is "right and wrong". Even worse, many of them are unwilling to listen or to try to understand. And, of course, they are quick to throw a tantrum like a 3-year-old. As a person who singlehandedly has to balance responses to all different users while providing great and timely support and developing new features, Kostya is sometimes forced to make decisions that minimize the inflow of those complaints. It is not a software-developer's decision, it's more of a business decision.
{philosophy}
Yes, it feels like the ignorance and breaking the rules get awarded in those cases. And it is not fair. But life is not fair. And, unfortunately more frequently then I wished, loud ignorant people get more than they deserve. (For that, just turn on your TV news on almost any day.)
{\philosophy}
As for Aquamail, - there is no ideal software that fulfills needs and desires of all and every user, but Aquamail got the closest to that. And Kostya has managed to choose the right balance for his app, listening to various sides, and making his own decisions. I might disagree with some of those decisions individually, but it is the entire combination of those decisions that allowed him to bring this app to this point, and to sustain it at this level.
You may feel mortally offended by this small "refusal", and I cannot do anything about that. But as a happy user of Aquamail (the software I am most fond of), I would encourage you to look at a bigger picture of what this app and his sole creator have to offer.
(This message was written before Kostya's more recent response that just got posted.)