If you read this article, you probably going to run into some trouble with a new
exim4 version.

https://debian-administration.org/article/140/Handling_mail_for_multiple_virtual_domains_with_exim4

this has a section as follows

vdom_aliases:
      driver = redirect
      allow_defer
      allow_fail
      domains = dsearch;/etc/exim4/virtual
      data = ${expand:${lookup{$local_part}lsearch*@{/etc/exim4/virtual/$domain}}}
      retry_use_local_part
      pipe_transport   = address_pipe
      file_transport   = address_file
      no_more


You'll need to replace the data section with the following to avoid getting a tainted file error.

   data = ${lookup{$local_part}lsearch{/etc/exim4/virtual/$domain_data}}