Expecting to receive a calendar invite from person who uses Outlook but the email comes in blank?

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.