[laurent92]

I wonder if Google has a backdoor API which lets group people by backup email. If one always creates an account with the previous email as a backup, the link is east to make.

That would be especially useful for censorship services across competitors: Although Google Facebook and Twitter compete, sharing the flagged accounts would allow recognizing the same user coming back with a different email address.

[vmception]

who said anything about backup email

but sure? probably if you just alternate between a backup email tied to an email you use everywhere