When I try to add my non-Google address as a Google account alternative email address, Google bars me with this:
I'm unaware of any Google account with which my email address is already used, except as as a recovery address which I presume is not grounds for this bar (esp. considering Google allows an address to be added as a recovery address without the permission of the addresses owner).
How can I find out which Google account this address is already being used with?
Note: This is not answered by either of: