I know this is a few months old, but I ran into the same problem and found a simple solution here, which worked for me. You just go to list emails, select the domain, and you’ll see a message with the “Fix Now” option. Clicking that seems to have fixed the problems for me.
I couldn’t figure out how to edit the above post, but ironically this post came up when I was searching for the same problem still occurring. After a lot of trial and error, I think I really do have it solved now - and it is not a particularly simple solution. It turns out that cyberpanel does not natively support IPv6
I don’t know if gmail always looks to verify an IPv6 address as the sender, or if it is only occurring because the server I provisioned has an IPv6 address. I had to add the IPv6 address manually into cyberpanel, add the domains I’m sending email from to that listener and then add the IPv6 addresses into my DNS settings.
I had the same problem. I guess whole issue was that I selected “Create Mail Domain” when created a website.
My server IP has rDNS of example.com, but CP created mail.example.com as email sender. Gmail doesn’t like email coming from mail.example.com and rDNS pointing to example.com
My solution was edit /etc/postix/main.cf by adding a new line myorigin = example.com next to existing myhostname = mail.example.com and of course Postfix server restart.
