Checking with google if domain is hosted on this server: FAILED

Hi,
I have limited knowledge and relatively new to CWP.
My setup is CPW7Pro hosted by me on my own local server.
I added some domains I would like to host and take care of the email.
The domain is registered and DNS is also handled at that ISP.
Followed the install instructions as far I can tell correctly. I was ab le to get one of the domains.
At DKIM & SPF Manager I get all (TrustedHosts, KeyTable, DKIM1, spf1, DMARC as OK)
However when I do the Domain checker for that domain I get all ok except that:   Checking with google if domain is hosted on this server: FAILED
I am not able to send or receive emails. Sending emails remain in the mail queue.
How do I fix this?

Thanks for your help

Do you have MX records in place? Reverse DNS with your ISP (PTR records)?

Is your local server behind a NAT?
Or do you pay your ISP for Public Static IP's?

Many ISP's also have SMTP ports blocked.

Thanks for the replies:
MX record is in place.
I previously checked all emails ports and port 25 is open and listening.
server is behind NAT. Other machines can be accessed
 without any problems as I opened my firewall to facilitate.

NAT's can usually only forward 1 port to 1 server, not multiple.

So for everything to work, you need to forwards all the common ports to that server, and then it may still have an issue as the server IP (Internal IP), doesn't match the External (Public IP).

So one of many, Reverse DNS will fail, because public IP 11.11.11.11 isn't resolving to 10.0.0.1

This will cause problems with email, and SSL.

CWP gives me:  rDNS/PTR record check: SUCCESS
I have a router and firewall with rules that should  take care of getting all port to the the right destinations on the LAN.
Not knowing the solution, but all mail related are currently pointing to the CWP server, so that doesn't seem to be the issue.