Well i'm the owner of domain.net and domain.com (fictive but i am an owner of two real domains) so i have configured my server as server.domain.net and asked my ISP to add a reverse dns record to my domain.
demo.local nad demo.biz aren't your domains and your isp's server won't allow it. That's like naming your server server.microsoft.com and sending mail from it. It can't and shouldn't work. You'll have to use a real domain name and dns records.
But i do admit that i have apropriate dns records and have never added a domain that i don't own so i can't test if it would send from your isp but i think that it wouldn't because of the dns issue (isp's server calls your server and it doesn't get a responce which is normal because you don't own the domain and the mail gets bounced).
Try a local domain and see if it works. And buy a domain, set the apropriate records and then report back.
It should work then.
DNS is working (it is using 192.168.2.1 from the DSL-router, and this one is getting it form the DSL-Dial-In-server)
Not your dns records.

Domain dns records. This isn't the same thing.