I would prefer a settings page where i can opt in oder out for certain mailings (if not mandatory) and set the timesettings myself.

Relying on the header information might lead to wrong results as some people changed settings and it relies on the browser. (Though i guess thats not valid for many users)

But while you're there, one can also set time to receive emails themself. Maybe i want to have it earlier because half of my tasks already need to be done by 7am.

Of course, the best is to combine both, having a settings page with default value gathered from the browser.

Nice article which really covers the problem many people aren't thinking about.