What is the reason behind the browser blocking custom redirect domain with HSTS in AWS SES?

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The reason behind the browser blocking custom redirect domain with HSTS in AWS SES is because the HSTS (HTTP Strict Transport Security) policy mandates that once a user's browser has seen the HSTS header, it will only connect to that specific domain over HTTPS for a specified amount of time (usually a few months). This means that any attempts to redirect users to an HTTP version of the domain or a different domain will be blocked by the browser, as it goes against the HSTS policy. Therefore, to avoid this issue, it is recommended to use the default Amazon SES redirect domain, which is already configured with HSTS.