The amount of newsletters you're about to send would require a couple of things:
- Server - most companies wouldn't allow you to send that amount of newsletters if you're using shared hosting. You'd probably need to get a VPS or Dedicated server with a lot of resources. I would suggest you having at least two. Also keep in mind your email server will be sending emails all the time and this will generate cpu/ram usage. So it'll be best if you use those servers only for sending the newsletters.
- DKIM key (due to the high amount of email you'll be sending daily your domain may get in spam filters)
- SPF records - needed to pass most spam filters.
When I had to do this, I had a quad core intel server with 4gb of ram. The amount of daily sent newsletters was around 35k. The server was specially optimized just for sending emails. The mail server was james mail server and I delayed mail sending - I had a daemon pooling about 15-25 emails per minute. That way the server load wasn't too high and I was able to bypass most spam filters. First I was using sendmail, but I started having problems with delivering some emails - they were being received a day or two after they were sent or they weren't received at all. I couldn't find out what was the problem so I switched to James Mail Server which handled the job great.
In my opinion you should focus your attention more on the server you'll be getting. You will need a lot of cpu, ram and network to be able to send ~200k newsletters daily. As for the email server - you need to try them and see which one works best for you. Plus, if you have a stable hosting infrastructure, you can easily change the mail server.
Also keep in mind you may need more than one server to be able to send those newsletters in time. If you want to send 200k emails for 24 hours, that means you'll need to send ~8333 emails per hour. That's a lot of cpu load. You may want to split jobs and have two,three or a botnet of server to handle the task fast.
I hope this helps.
P.S. Look at the post @hakre added as a comment. You should also consider using the services of MailChimp and other alternative companies who offer this kind of services.