Check out sendx.io They are really affordable, you have to pay as less as $7/month for 1,000 subscribers. They allow you to send unlimited emails across all pricing tiers.
sendx.io is a cost-effective option you might want to explore. They have a good resource on open rates for email list more than 100k, check here if this helps https://www.sendx.io/blog/email-list-managment/
You can only reach out to people who have Opt-in as per CAN-SPAM, which means avoid sending emails to folks who have not opted-in. Maybe if you are looking at relevant tools to help you with opt-in, check if this helps https://sendx.io/blog/using-mailchimp-alternatives/
You can try SendX.io I've been with MailChimp for long but shifted out due to the high cost and poor support system. Before settling with SendX, I've tried getresponse and mailerjet. However, found SendX to be more affordable and easy to use. Especially, their email automation piece is straight forward to setup.
Try sendx.io It is one of the cost-effective platforms that allows you to send unlimited emails. Be it bulk mail or pure-play email automation, the features you get for the money you pay is just amazing.
There are umpteen numbers of providers that let you send an automated email. Few providers like sendx.io even offer free trials. Give this a reading to understand how you can make the most out of automated emails https://www.sendx.io/blog/email-marketing-automation-strategies-optimize-marketing-funnel/