[exim] Router: check for domain in list

Hi list!

I need to check, in a Exim-Router, if the sender domain is in a list
of domain.
I tried so:

condition = ${if eq{${lookup {$sender_address_domain}wildlsearch
{/etc/exim4/virtualdomains.txt}}}{}{yes}{no}}

but it does not really works...
The file /etc/exim4/virtualdomains.txt is just a list of domains, not
a key:value list, so such this:

/etc/exim4/virtualdomains.txt:
domain1.tld
domain2.tld
...

I really don't know which other lookup I can try to just check IF a
string in a file exists.
Can someone suggest me somewhat?

Thanks
Luca Bertoncello
(lucabert@???)