Keeping data consistent, compliant and true is pretty hard nowadays. We are aware of legacy code and tech debt problems, but rarely concern ourselves with data debt . This problem doesn't show much if you have a 100% subscription business and you delete users whose subscriptions have expired .
Source: [Dev.to](https://dev.to/berislavbabic/keeping-your-email-deliverability-high-by-filtering-invalid-email-145d)