What are the minimum requirements for inbound mail flow?

Question

I'm working on a server and want to send out mail either from a form to email or get email address from database then send..

I'm using PHP mail(), currently the mail send out fine with simple PHP mail() but do I need to us PHP mail() and some kind of SMTP Authentication to lock it down?

PHPMailer or some better way? do I need to install something like this on the server?

https://github.com/PHPMailer/PHPMailer

If so what's best with PHP mail() ? or is there some more modern way to lock it down...

Answer 1

The following are the minimum requirements for inbound mail flow:
Exchange Server must have access to the Internet on port 25. This access should not be blocked by firewalls or other network settings. Anonymous connections should be allowed.
The Exchange Server SMTP virtual server should be configured to use the default settings. For more information about configuring the Exchange Server SMTP virtual server, see Microsoft Knowledge Base article 266686, How to Configure a SMTP Virtual Server Part 1.
The public mail exchanger (MX) resource record configured on your public DNS service should be accessible to all other Internet domains. The MX record should point to the Exchange server and must be identified before messages can be sent or received.
Recipient policies must be configured and applied correctly. Recipient policies will stamp the SMTP virtual server and the recipient's mailbox with the correct e-mail address.