I've been wrestling with it's email functions for a few days. I've been getting the dreaded "Load 25 more messages" prompt when checking my Yahoo mail. System updates and restores did nothing to fix the problem. I finally found a work around, here was my solution in case this is happening to you:
Step 1) Create a 2nd email account on the iphone. I used my already existing G-mail account.
step 2) Open yahoo mail on your mac (or PC) and create a new folder & move all of the messages in your inbox into that folder. I had 10,000+ messages so it took a few minutes. Your yahoo inbox should now be empty.
Step 3)Open your 2nd account on your iphone, and send yourself a test message, to your yahoo mail account.
Step 4) Wait for message to appear on your iphone! :)
Apparently, having a ton of old messages cluttering your inbox confuses the iphone. Moving them to a new folder solves the issue. The only draw back is now you have to switch folders to find old emails... :)
