I wasn't sure where to put this - I've posted in iOS 9, but I'm actually having exactly the same problem on my MacBook. The problem is: since sometime around last Monday (25 Jan) I have been having trouble receiving email on my work account (Exchange). Some emails were coming through straight away, but sometimes a whole day's worth of email was being delayed. I've now worked out that the problem only seems to be when I'm using mobile data. I'm getting no error messages, emails simply aren't arriving. I should mention that I have several other email accounts on my devices (iCloud, gmail etc.) which are working fine, so it seems to be just the Exchange account. I spend most of my life using mobile data through my iPhone or separate mobile wifi hotspot, so not receiving email is becoming a big problem. I've asked the IT people at work, but they don't seem to know. This also isn't a signal strength issue - I have a 30MB/s 4G connection. Has anyone else had this problem or know of any solution?