@AKLBlue: Please post the exact error messages that you get in the mail.log.
@ma...; Your problem is different as you can login to your mail accounts according to the log. Your problem is that you used a wrong hostname for the server. The server hostname may never be identical to a domain name that you want to use for email. Open the postfix main.cf file and /etc/mailname file and replace yourdomain.tld with a subdomain like mail.yourdomain.tld and then restart postfix.