How to send 1 million emails per day?

I'm curious, could you elaborate on the practical steps and considerations involved in sending out a staggering 1 million emails per day? What kind of infrastructure or software would be necessary to achieve such a volume, and how does one ensure the emails are delivered effectively while also adhering to anti-spam regulations? Additionally, are there any potential challenges or pitfalls to avoid when scaling up email marketing efforts to this level?