We have a situation where a client's external meeting requests are being received and displayed with nothing in the “From:” field, except a colon.

When accepted, the appointment still shows nothing in the “From:” field.

When viewing the properties of the appointment, the “Created by” user is correctly listed

The header info appears to be correct when viewing the email header in an editor, and from our mail filter administration utilities.

Our client is using Exchange, but I am not sure what version.

I am not sure where to go from here. Any help would definitely be appreciated.