Some important functions disappear at certain levels of screen zoom
Because of my eyesight, I often increase the zoom on my screen. In this new design, certain essential buttons disappear "below the fold" and require either a scroll or even resizing the zoom level so it appears. This includes the list of MAILBOXES at bottom left and also the SEND button when composing a message.
These crucial functions should either be moved up to the upper part of the display or remain durable at the bottom of the screen regardless of the level of zoom. Or at least allow the left panel and the overall page to be scrollable so we can scroll down to the Mailboxes button and the SEND button.

-
Doug O . commented
I agree with user "e hoff" about the message field needing a horizontal slider! Plus, the entire page needs one as well. The SEND button gets hidden below the bottom of my screen, as I mentioned above.
-
e hoff commented
The full email message in the center box does not display on my (smaller) laptop screen. Only the left hand side of the message displays. The right hand side of the message is hidden behind the ads. (Of course, the ads are always shown in full!) There is no slider to slide the message to read the right half of it. The only way to display the message is to zoom out to a tiny font that is not readable. Yahoo needs to add a slider to the message or fix the proportions of the screen boxes.