I've been fighting with this since last night and have tried just about everything, including a restore from the backup prior to upgrade and deleting my iCloud account. I also have two Yahoo accounts and one works fine, but the other doesn't download mail after 9/13 and push doesn't work with it. I finally deleted all accounts, added back the yahoo that wasn't working, it still didn't work, so I deleted and re-added it and now I have current email; not just email from 9/13 and back. However, when I sent a new email message to it, it takes a while and says Checking for Mail and doesn't get the new message. Once it said Downloading 1 of 1 but then didn't download it. When it was only download from 9/13 back, it sometimes said Downloading 1 of 84 and got up to 3 and quit, then would say No New Mail upon subsequent checks. Someone please figure this out!