How do services like Substack and Beehiiv send email?
I'm looking to start a similar service, can I just use a bulk mailing API like Mailgun?
Is that how it works?
Pretty sure substack uses mailgun. If you dig substack.com for mx and txt records you’ll see that their spf includes mailgun and their mx records point to the same as well.
Can you not use sendmail with appropriate DNS/DMARC records flashing the requisite badges? No need to make more work for yourself.