According to Product Manager Stephanie Shum Sr. from Yahoo! Mail has written on yahoomail blog:
Now Yahoo is introducing a few new features for Yahoo Mail Beta users. Those running the latest version of the popular webmail interface already have a number of unique features and the updates continue to improve them.
Giving you more message space
We’ve been hearing a lot of feedback from you about how much space the purple header takes up and how it limits how much of the actual message content you can see at once. We still want to provide some room to showcase our existing and future themes at the top of the page, but now you can scroll the entire Yahoo! Mail page so you can see as much message content as possible. Just go to Options>Mail Options and select “Scroll content of the entire page”.
Along with the ability to scroll the entire page comes another way to view your inbox. For those of you who are coming to the Beta from our Yahoo! Mail Classic product, we now have a paginated Inbox list view that might look familiar to you. You can view 50 messages in your list and click to go to the next, previous, first or last pages. When you click on a message subject line, we’ll load that message in a full tab. You can change the number of messages per page by clicking on Options>Mail Options and then selecting from 50, 100 or 200 messages at a time. If you still prefer the preview pane mode, you can also change this setting by going to Options>Mail Options and selecting “Scroll each panel on the page individually”. Try it out and let us know what you think!
Access to your past IM conversations
I don’t know about you, but my friends are always, always sending me important links, dates, addresses and other tidbits of information via IM. If you’re anything like me, you’re always, always forgetting exactly what was said/shared. What restaurant were we supposed to meet at? Where is that hilarious link Mike sent me about iPhone autocorrect fails? I rely heavily on my archived messages on the Messenger client and am so excited that we now give you access to your past IMs in Yahoo! Mail Beta. Just click on “Conversations” on the left side just below “Inbox” and see all your past IM conversations from Yahoo! Mail Beta (and the latest downloadable Messenger client).