On the billing model: The service I had was charging me per email sent out – so, while my emails were only getting to a few hundred people, I was paying to send 2500 emails. And I send them out twice a month, so I was paying for 5000 emails and only getting about 800 delivered. Less than 20%. 

This is one of the two major billing models, and wouldn't be so bad if the deliverability rating was better. But, there was one big problem outside of that issue with how this was being charged.

When I looked at my list, I discovered I was actually being charged for everyone on my list, including addresses that had "hard-bounced" – which means that the address no longer exists – and people who had unsubscribed. Which seemed pretty ridiculous.

I've now signed up for a service that bills by the month, and bases that price on the number of subscribers on your list. But, you can send out as many emails per month you would like to your list during that time – so if I need to send out 3 emails in a month, I would still get billed the same amount. That seems much more reasonable and flexible for a regularly-recurring newsletter.

The instance where the pay-per-email model works better is if you don't send out many email newsletters (for example, if you send out 1 per month, or 1 per quarter, or if you have a very small list, that model can save you a lot of money).