I wanted to find out too, how much of my email is in the hands of Google.
Whole email archive
I haven’t very carefully archived all my email since 2007. For what preceded 2007, I was using email through OVH’s POP server and I didn’t really care about archiving email, so that’s lost.
What’s interesting is that the proportion of Gmail is higher when I had the highest quantity of email.
However, the Gmail proportion might seem particularily low because most of it involves people active with the Free Software Foundation Europe. However, it’s still much higher than Karsten’s.