I have the same problem and feel sick and tire with it, I find the problem may not in the email client but the phone's internet connection. I set up auto retrieval every 5min. and it worked fine until I upgrade to current firmware, now it won't check mail as set, I can't predict when it will check. I see that some time it tried to check mail but the 3G link is not up, I must manually send and receive to do it, so I missed many mail. I've the same problem with older N phone as well, the internet connection did not go up as needed.