I had an old gmail acc, that was used for various registration and confirmation tasks for almost 2 decades and mostly never for composing emails, but recently, smtp and imap access to it disappeared.
Ok, I'll keep you as a reverse proxy forwarding incoming messages to one of my actual mail boxes for a while, but won't spent any more minute to workaround your proprietary buggy behavior. And hack off with your "security" enchancements, my dear privacy-respecting bigcorp.