Starting from 2015-11-12, emails started working again. In my application, the code was not changed, and emails started to work.
However, Invites posted yesterday are still lost.
I can only put it on a problem with the Google service.
I guess Google App Invites is still in beta.
I mark this answer as βacceptedβ after a few hours ... just in case, when someone from Google reads and wants to comment and confirm what the problem is.
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