"Gmail will continue to receive emails from non-Gmail addresses"
twitter.com
twitter.com
[1] yes, "ignore" - they didn't even bother sending a NAK, so subscription requests end up looking still-pending or lost from the outside
Coworker beside me: "I just sent you that thing."
Me: "Great, let me just go to settings, accounts, scroll to my work account, and click 'check now' so I don't have to wait half an hour"
Oh well, You might say it already happened: Whatsapp, Facebook Messenger, etc.