There are many types, but the emails have a single goal:
SELL.
For this, you need to involve and nourish the subscribers, so they do not get bored reading them.
Otherwise… bye-bye.
They go to someone else (perhaps your archenemy), and you will think to stop.
Please don't do it!
Let's transform them from simple (shy) subscribers to (die-hard) buyers and readers.
So, when you want to sell or launch a product/service, they will be ready to buy it.
I will write any email you need!