Here is a notes for Email Server Settings. It is not just for Email server. It is mainly for DNS setting for Email server.
The purpose of it is to prevent from your outgoing email into spam box.
I have a web page, which use PHPMailer to send email. The problem of it is most of time the recipient found the email in the spam box. I am using sendmail to send out email.
Later I choose to use ZOHO as my email service provider. And choose smtp in PHPMailer.
So, the solution is here for ZOHO.
- SPF record