Exchange - Automatically downloading attachments

Hi,

I'm seeing an issue with our iPhones, where attachments are automatically being downloaded silently in the background as soon as they're received.

I've done some testing, it's happening consistently with our whole fleet of iPhones (about 150). It's costing us money when our users go abroad as they're using so much data.

• Issue appears to be with an device with 9.0 upwards only
• Only with Exchange mail, 2010 SP3
• IMAP Gmail doesn't behave this way
• iPhones with 8.4, 8.3 don't behave this way
• Have tested with iPhone 6 and 5S
• Downloads attachments silently and instantly as soon as the email is received, it does so on Wi-Fi and mobile data
• Doesn't seem to matter what the attachment is, it will always download

Has anyone else seen something like this?

Thanks,

Dave