I also have this problem which started yesterday. The emails synch OK on WiFi but fail when connected to the 3G. This happens with both an Outlook and Yahoo mail account on the iPhone. These are both IMAP accounts. I am unable to send mail and download new mail to either account. It feels like a port has been blocked on the 3G preventing the mail from connecting properly which would explain why it works OK on a WiFi connection. Hopefully someone at Virgin might have the answer?
Wend50, try uninstalling, rebooting the phone then reinstalling, that allows for the setting to be removed from the phone
Andrew, your issue is very different, iPhone are a strange beast in some ways, if the phone works on wifi with no dropouts there should not be an issue over 3G, provided you see the 3G or H reception icon
from googling on this the consensus is that you have an incorrect setting on the email
Thanks very much for your replies. I got to the bottom of the problem this morning. Quite simply, within Settings > Mobile Data, there are options to specify which apps Mobile Data can be used for. In my case, Mail had been disabled, hence email would only send/receive over WiFi.
With Outlook.com accounts, I do remember there was a time when this setting made no difference as they were based around Exchange ActiveSynch and would continue to use cellular data even when this setting was disabled - https://support.apple.com/en-gb/HT201299
It looks like something has changed with the behaviour of Outlook accounts now, and obviously this setting needs to be enabled for email to work on cellular.