As I always say, the best setup to have great results (>70% open rate) is not by using custom SMTP / Mailwizz or other shitty big blasting tools.
I don't understand you guys of being proud to send 1M or 200k emails per day. It means nothing.
Sending 1M per day and having 5-10% open rate is a really bad result.
Do you wake up each morning to break the record of the highest number of emails sent ?
No. You wake up each morning to grow your business.
To get a badass growth, you need to have good email results.
To get good emails results, you need a solid email reputation / email deliverability.
And you don't have a great deliverability by sending that much emails, that sucks.
You get great results by acting human. A human does not send more than 200/300 emails per day per email address. A human uses a real email inbox and does not rotates IPs. A real human (who doesn't spam) has a high level of engagement on his emails. That means his emails get opened, clicked, marked as important, replied, removed from spam if needed.
Conclusion : send from Gmail / G Suite accounts, use MailShake to automate the sending, use Mailreach for your deliverability / open rates.
A part from MailShake, that's my setup and I get more than 70% open rate of average for each of my customers. I do this without having to spam all the planet.