Someone asked me to send them an Outlook invitation. I'm not on Outlook and don't want to set up an email account just to send them an invitation.
Is there a way to send an Outlook invitation from Gmail?
There is no specific invite for an Outlook user within the default Gmail interface. Since you can send a calendar invitation within Gmail now testing the behavior of Outlook should be trivial.
Generally speaking varying clients such as Outlook, Lotus Notes, Thunderbird, etc... acknowledge the invites from a differing client; however in some cases they don't.
Based on information from this thread it appears that at least towards the end of 2007 they stopped working; going from Gmail to Outlook.
The best option is to simply send a standard calendar invitation within Gmail to see how Outlook responds.
I just tested this by creating an event in my Google Apps Calendar to my Outlook 2010 calendar at work. It successfully came through as a calendar invite, and upon accepting, it was added to my Outlook calendar, Google calendar and the acceptance response email was received in the GMail.