I wouldn't say none, you still need to setup your DNS settings with SPF/DKIM to support Mailgun/Sendgrid. They usually have documentation how to do that, but you need to be sure to do it. :)

Good article though... overall, if you aren't in the kind of email volume you guys are, just use Sendgrid/Mailgun. Sending email is a PITA and just pay someone else if you have the option. :)

PTR too. rDNS is important.