What about web traffic?
If I forward the domain at the registrar then the email will never reach my server so ISPConfig will not be able to forward the email.
If I do not forward the domain at the registrar and use ISPConfig to forward the email as you suggest, how can I forward the web traffic?
Each web page on the old domain must forward to the same webpage on the new domain like this:
olddomain.tld/index.html > newdomain.tld/index.html
olddomain.tld/folder1/index.php > newdomain.tld/folder1/index.php