I develop all my own software. Search BLPREI on youtube for an example and my software does much more than what you asked for.
Mailchimp is useless because Mailchimp requires that your email list has only opted-in email addresses. So, you cannot use mailchimp to send tens of thousands of emails. Even if you can get email to send your email list that is not opted-in you have to pay a hefty price and working with mailchimp is time-consuming and more cumbersome than sending your email with your own software Atomic Mail Sender.
The best place to get a list of foreclosures is auction.com and this is in the youtube video.
The best place to get email lists is datazapp.com, but there is no good foreclosure list you can buy from any source for foreclosures with the exception of auction.com (that is free) because 95% of all the pre-foreclosures on other lists are cancelled. That means 95% of your time, cost and effort is 100% waste. Auction.com gives you a list of pre-foreclosures that have an actual auction date and even 90% of those get cancelled before and on the day of the auction, but, at least, you have a better chance.
For sending tens of thousands of emails every month for free, I use Atomic Mail Sender. I think the software costs about $79. Combined with my own software, I send 4,000 emails every morning between 6 am and 7 am and it does not cost me a penny with the exception of purchasing the email lists.
At first, about 25% of the email lists I purchased had had email addresses. I purchased 150,00 email addresses. That means about 35,000 email addresses were rejected and returned. So, I paid girls in the Philippines 3 cents per email address to remove the bad email addresses from my database. Now, when I send 150,000 emails I may have only 10 or 15 rejected.
Quickbooks sucks and I run several businesses with software I developed, myself. Someday, I will post a video showing my bookkeeping system that is so simple it can be set up in less than 1 minute and so accurate my records are never off by one penny. But, I've been really lazy about posting it.