is the message blank even if you check it through webmail?
Yes. From another user of Outlook it is just fine though.
I have the same problem. invites sent from Outlook does not show in em-client, but is fine in gmail.
I have the exact same issue in the included email client in windows.
After some research I have found this is related to em-clients rendering of TNEF-formatted emails.
The company I’m working for are using both exchange and google apps with the same email domain. When a coworker using exchange sends invites to my gmail-account the invite come in blank. When the same coworker sends invites to my private gmail account the invite shows as it should, because outlook uses ical-invites when sending to adresses outside of the domain.
Since we both have the same email domain, outlook formats the invite as a TNEF-message with the attachment winmail.dat but the invite is not understood by em-client. I can send an example if you want to.