How much can you earn from paid emails?

I'm curious, just how much can one potentially earn from participating in programs that offer paid emails? Is this a viable source of income, or is it more of a side hustle? Are there any specific requirements or qualifications needed to start earning from these emails? And what kind of earnings can one realistically expect? I'm looking for a clear, concise answer that can help me understand the potential benefits and limitations of this earning opportunity.