We must also distinguish:
- newsletter: that is to say a regular mailing of a digital magazine (basically a web page) to its own list of contacts.
- emailing: a commercial mailing to a list, either his own or that proposed by a provider.
I once tried a provider, sending a message.
I've been disappointed.
What's funny is that he added my email to his list, so I received my own message, but in spam, and more impossible to open (empty content).
So, if I trust a provider in the future, he will have to prove to me that he is a professional.