I've got a user with a Palm Pre, syncing to Zimbra via Zimbra Mobile / EAS (NE 5.0.18).
Some of his messages (maybe 10%) come through with no sender name. For those messages, the Pre doesn't allow him to reply or forward the message - the options are greyed out.
There are two posts on Palm's forums (below) that mention the exact same issue with Palm Pres and Zimbra Mobile. However, there are no replies.
Sender Missing on Several EAS Messages on Palm Pre - Wireless Email - Palm Support Community
Can't Reply or Forward Messages - Wireless Email - Palm Support Community
Anyone else seeing this issue? Anyone have any other info about it?