We have huge number of email list, recommend tool to send mass mailing ( 1 to 2 million email a month) without any issues.
I used mailchimp once upon a time on my website. It was an elearning website where we used to send newletters every week, we had 50000 email subscribers on that one. Cost us a bomb to email people. I then switched to Amazon SES for sending emails. 1$ = 10000 emails if your website is also hosted on ec2, for 1 million emails it ll cost you 100$ a month. SES obviously only handles the logistics of sending. Email campaign management, user list management is also a huge requirement which is covered by Sendy, You can actually Google Sendy SES integration and find a bunch of videos on that. Send costs 59$ / major upgrade meaning 4.0.1 to 4.0.2 upgrade is free but 5.0.0 would cost you 59$ again. It is a one time cost per major version.