Email clients not connecting

Hi,
After creating account and updating the server names, I’m experiencing issues with the email clients that cannot connect to the host. I’ve checked your tutorial and the other topics in here, with same issue, but for some reason I still cannot fix this. All DNS records seems to be as advised (see the screenshot below, with no success. Could you please advise what can be wrong

That’s a functioning mail server, but it’s extremely slow. Make sure your mail clients are configured to connect to the ‘mail’ subdomain and not the root domain.