Sending out bulk emails in a timely fashion without getting blacklisted or flagged as spam requires an email service with a high domain reputation and a sophisticated mail dispatch algorithm. Mailchimp just happens to be one of the more popular ones, but there are plenty of alternatives.
There are open source tools for email list/newsletters, including throttling, that you can install on your server. There are a couple of free or cheap services to run an email through that detect the spamminess of them but that’s a matter of good writing skills and not too many links. All emails must have a one click unsubscribe link which is basic etiquette. There are also free services to run your domain name through that will tell you how well the server is set up as far as trusted standards. I’ve done all of this on my own and I had an email list with a few thousand back in the Tea Party days. Every email went through and I gained subscribers when emails were shared/forwarded. Email hasn’t changed much for many years. 600px wide max and send both html and text versions. I also build websites. The bee runs wordpress and there are tons of solutions for that. Sending via SMTP instead of phpmail is important and that’s super easy.
That’s all pretty basic stuff. What’s extra that mailchimp has to offer is that it can connect to and/or track your social network accounts as well. They also have a lot of data for demographics, best time of day to send to a particular group, analytics etc. That and you don’t have to learn which is a big plus for most people today. Just click a button, sign up and start paying. We’ll hold your hand through the rest.