just to let you know that I RESOLVED this.
It HAS NOTHING TO DO WITH YAJHFC. It was a hylafax server configuration
tidbit I missed.
In my defence, this is the first time I had to configure this specific setting.
I have three hylafax server installations from which this is the only one that
red-flagged this !
So here it is, very clear at the end of this page / link :
The only machine that talks as a client to hylafax is the server itself as "localhost".
If you want to add more machines / nodes / networks / subnets, you have to
explicitly state them one by one.
I tried the regexp line that it has at the bottom :
and changed it to this :
in hope that it will allow nodes under 192.168.20.0/24
to access the server and it did !
Restarted the hylafax service and everything worked fine.
Thank you all again for your time and patience !