Function adopt_one 

async fn adopt_one(
    services: &Services,
    server_name: &ServerName,
    bound_at: MilliSecondsSinceUnixEpoch,
    localpart: &str,
    address: &str,
) -> Result<bool>

Binds one foreign row, reporting whether it produced a binding.

A false return is a row with nothing to bind: an unusable localpart or address, an account absent here, the server’s own, or an address already held by a different account, which this store cannot represent twice. An error is a read that failed and must not be mistaken for any of them.