Working on DNS for using Mailchimp

This is something it came up lately, I was just trying to figure out for some friends that they wanted to use Mailchimp to send their newsletters but apparently, there are some settings to be done. But thing for me, as I had already tried to use the service unsuccessfully with my email server, I found out from them that a DMARC issue was there. So, I lately wait for the DNS to sync and for Mailchimp to verify the changes. I hope this works even if I don't use the service for me.