Thank you Shabbir for quick response again.
I would like to redirect people automatic to the blog domain. If they can see that they are redirected or not, is not important. Just to move them to the subdomain and open the wordpress blog I have there. But also to keep it SEO friendly.
The thought is to keep the main domain empty at the moment, to be able to use it in the future.
If there is no simple way to do this I will rather move my blog to the main domain.
I hope you can help me and that you now have enough information about it.
Best regards, Jan