Lately I have been getting an increasing number of complaints regarding users not being able to download attachments synced from Exchange with their iPhone.

The iPhones in question are either 3G or 3GS with firmware 3.0 or later. Exchange 2007.

The majority of messages come in just fine. Some however display: "This message has not been downloaded from the server" where the email's text normally should be. At the bottom of the email, it states: "This message is only partially downloaded." It has a button labeled "Download remaining 0 bytes." If you click this button, it states that it is loading and then reverts to the same screen.

The odd part is that this only affects some emails. Most come in fine with attachments working.

I've taken the same email that was not working on my iPhone. Sent it to a gmail account that my iPhone had access to. The message and attachment opened fine.

Any ideas of possible causes I could look into?

Thanks.