Mass Email My Members (500k)

I'm currently owning a website with little less than 500,000 users. Many of these users have been asking if I could send out updates about the site per email, like once per week or preferably once per day.

I'm not sure about the best way to do this. I did some reading and some people seem to suggest to get an extra dedicated server to send out the emails. Others say it's best to use a cloud service with SMTP relay, while I also saw suggestions to use a website like [url]

I have checked into mailchimp, and appearantly this whole thing will be very expensive if I want to send out email to so many users. I'm not an email marketeer and neither do I sell products, so the profit per user I would email is probably low. The primairy reason I want to send out updates is to keep my current memberbase happy, and to get some older inactive members to become active again. We had our site totally reworked recently, and it would be nice to let people know about that.

I also like to know if it's possible, in any service, to somehow unsubscribe users whos email addresses are no longer valid in an efficient way.

Some more facts:

- Those 500k users are 250k effective emails. The other people have never subscribed on registration, are blocked for misbehaviour on the site, or have unsubscribed at some point.

- As stated above, people have to subscribe upon registration. The checkbox for this is unchecked on default

- The oldest users in my database are 3 years old, so there is quite a chance emails might be no longer active.

- There are many scams in the industry I'm active in (survey panel). As a result, users are sceptical, and sometimes use alternate email addresses for registration. I believe that as a result of this there is a higher chance the email is nog longer in use than on other sites, although I have no stats of other websites to compare with.

- I once tried to send out email to 75k users on my current dedicated server. As a result, Yahoo deferred my emails (which caused trouble for the verification emails we send out upon registration). I contacted Yahoo and they whitelisted my server, but I don't feel like trying to send email from my current dedicated server again. Not to mention that the server had a lot of trouble sending out so many emails, the server load was really high while sending out all email.