Postfix for dummies: how to set up one exclusive incoming mail address?

[Heinz Hummel]

Hi,

on my server there are currently some PHP-scripts (mainly contact forms) which only send mails to recipients. Here the person who uses the contact form gets a notification mail and the addressee gets the message. The notification mail is sent from an address nor...@domain.tld where domain.tld is a valid domain with SPF entry, DMARC-record and everything that is needed nowadays to ensure the mail arrives.

Currently this server does not accept any incoming mails, means bounces to nor...@domain.tld are ignored.

Now I want to change the configuration of Postfix to receive these bounces. Means I want to set up the server in a way where (returned) mails to nor...@domain.tld are accepted - but without creating an open relay or opening other security holes.

Any ideas/hints/tips/tutorials how this can be done securely?

Thank you in advance for any helpful comment :-)