Emails are sent using your own AWS SES account, which will handle all of that. No real concern of people sending spam because they would be damaging their own SES reputation.
I don’t even like MailChimp but there’s a real reason to use an app like them/similar. They help you not screw up "all of that" is complicated.
Typically via ReturnPath. It’s basically a scam, but everyone pays for it.