Yahoo Mail Always Checking for Mail
A few days ago I upgraded from my old iPhone 3G (OS4) to the new iPhone 4S (OS5). I have previously used the Yahoo Mail app to get mail on my 3G with few problems. However when I loaded the Yahoo account/app onto the phone it would not stop checking for mail. Even when I put the phone on standby and thought the mail program was off, it would keep checking in the background and thus drain the battery quickly. Also, while the mail was constantly checking, the phone would not send outgoing email. The problem also stalled any other email accounts I had installed (like gmail) and would not let them download either. The problem was somewhat random in that sometimes it would download the Inbox okay, but hang on my email folders. Sometimes it would download some of the email in the folders, but hang on the Inbox. Etc.
I spent a few days working on this issue by searching the web for solutions and spending some time with Apple Support on the phone and in the Store. After much trial and error, here are things that did not work, things that worked temporarily ( a few hours then the problem came back), and finally the one thing that seems so far (12 hours) to be permanent. I do believe the problem lies in the way the Yahoo account/app interacts with the iPhone 4S and is not exactly a outright bug, but who really knows?
Things that did not work at all:
Uninstalling and reinstalling the Yahoo account (a zillion times)
Rebooting the phone.
Reinstalling the entire OS5 of the phone.
Running the Yahoo Mail on a Apple Store phone.
Conclusion: the phone was fine; it was a Yahoo Mail problem
Things that worked temporarily:
Deleting all unnecessary emails and email folders in my Yahoo account from my computer (some forum users have reported finding "corrupt" emails that hang their systems).
In Yahoo Mail on the computer, set Options->More Options->POP&Forwarding->When POPing messages->include spam messages and add [BULK] as prefix to subject. (I previously set it to "don't POP spam" but the Yahoo mail sets up on the phone with a [BULK] (i.e. spam) folder automatically and I thought perhaps the phone was looking for the [BULK] folder on the server but wasn't allowed in by my former settings and hence got hung up).
Unfortunately, the two above solutions appeared to work at first, then several hours later the problem returned. But they gave me clues that perhaps it was something in the way the phone was searching the Yahoo server for messages and not finding something it was looking for.
The thing that finally worked so far:
On the phone->Settings->Mail,Contacts,Calendars->Mail->Preview-> set to None. (The default is 2 lines, I also tried 1 line, but the phone still hung).
By not trying to preview the email contents, the phone now seems to Check for Mail then stop after downloading anything new, both in my Inbox and all my folders. I have been testing this over the last 12 hours or so and its seems stable and my battery is not constantly draining. My tentative conclusion is that somehow the Preview feature on the 4S does not work well with the Yahoo server. (I worked fine on my old 3G, go figure).
Anyway, for me this has worked for now. Hopefully it will continue to work. I can live without Previews, but not without my mail :-)