It seems that more thought has been put into how the interface looks on a smaller screen (smartphone or tablet, for example) than how it looks on a regular size screen (computer or laptop, for example).
I understand that space is needed around buttons to make them easier to select correctly, but it seems that space is wasted otherwise if used on a regular size screen.
Gmail offers “Display density” in their settings - Comfortable/Cosy/Compact
Is Runbox considering something similar in Runbox 7?
Not yet, but that is a interesting suggestion! 
Kim
+1 I like this suggestion… would be very nice to have a display density option so we can adjust for taste. Perhaps add a font size option as well. I find the current layout to be inefficient in terms of screen usage compared to other email apps. It looks nice though, but display density + one or two font sizes would be nice.
R7 looks good on my personal notebook (15") lower resolution (older notebook) but my work notebook that has a 17" screen and is high-resolution 1920X1080. This really exasperates the fact that the floating bar is pinned in the lower right of the screen (spam, move, and delete). This must just be a bug or not implemented but the delete key does not work to delete selected messages.
I too vote for this. I do not like the way a lot of websites are making their interface pretty for touchscreen devices. My banking for example, i used to see all my account details on one screen. Now everything has big buttons around it and i have to scroll through 2 or 3 screens to see the same information i used to see on one. If there was a way to compact the view so i could see more on my computer screen, but have the ability to make the buttons bigger for touch screen devices should i use one would be good. While the new interface is nice i find everything is spread out more. Taking more screen real estate than i think should be necessary. Perhaps for tablets and iPads the new layout works great, but for us other people who use a computer with a mouse and keyboard, it is less interesting.
Interesting discussion, and I agree with several of the points made.
When we designed the Runbox 7 interface we wanted to start from scratch and avoid sticking to the principles of Runbox 6 where we tried to put as many messages and menu items into as small a space as possible.
With modern technologies it’s easier to make interfaces responsive and only show functionality when you need it, and since screens are typically larger (except for phones and tablets) there is more room to “breathe” and that’s why there is more white space.
We will continue tweaking the interface to make it user-friendly on both large and small screens.
I want to second this. I think your current system actually allows for different layouts. While this one is good, it’s too big for me, and I can’t see all my folders on the left anymore. I like things more compact, and find myself not using the new interface because of this and other visual issues. It’s just too big and undistinguishable with the bold and “normal” weighted fonts being too similar. It all smudges together in my head, and I can’t pick the important from the secondary.