The e-mail funnels structures vary a lot depending on the purpose and business models. For example, I've mostly seen better conversion rates with shorter sequences for B2B models directed to big/medium-sized enterprises, as they should be part of a hybrid, overall longer funnel that builds authority and position the brand, before closing the sale.

Other common approaches for B2C and B2B towards small businesses

4-6 Emails a month for a newsletters campaign

2-3 emails a week/in two weeks for discounts and product launches

4 to 8 emails over 2 to 4 weeks for cold conversion funnels