Whitelisting mailchimp verification email after following full email server tutorial.

I have followed every step in the Build an email server from scratch series, and have a sucessfully working email server. However, I am not able to get certain emails, specifically ones from the mailchimp email verification process.

I have whitelisted the domain:

in the following files:


and for some reason, the verification emails from mailchimp to verify my email address, are bouncing.

Here is the message from mailchimp:

What am I missing in the whitelisting process? Are the other files that I need to touch and add domains to in order to get a whitelist for this domain going? How can I prevent these emails from bouncing automatically? Or at least, move them to my spam folder?

Any help is appreciated.