[Exim] Using Expansion Variables in Regular Expressions

Hi Folks,

I am trying to construct a regular expression, which is to include, as part of
the expression, the contents of an expansion variable ($sender_host_name),
with appropriate escaping of periods in the hostname.

My first attempt is:

{\N<partial regex>\N${rxquote:$sender_host_name}}

Any advice appreciated.

TIA

Jim Roberts