[exim] untaint assistance

I would appreciate some assistance on untainting the following router:

virtual_client_addy:
   driver    = accept
   transport = client_mail
   domains   = cdb;ETCDIR/virtual_localuser_domains.cdb
   condition = \
        ${lookup{$local_part@$domain}cdb{ETCDIR/virtual_localusers.cdb
{yes}{no}}
   log_as_local = false

a previous email (2020-11-07 Michael Haardt) suggests to " use two
lookups, one for local_parts and one for domains , even if both perform
the same lookup "
I DO have another cdb file: virtual_localuser_domains.cdb ( if that
can be utilized ) , but the original cdb referenced above contains the
complete customer email addy ( addy@domain )


above router uses the following transport:


client_mail:
driver = appendfile
lock_interval = 30s
create_directory
delivery_date_add
directory_mode = 0700
envelope_to_add
file = MAILBOXES/VIRTUAL/${domain}/${local_part}
group = mail
mode = 0600
return_path_add
user = mail

I imagine , once the router is corrected , the "file =" in the transport

will be:
file = MAILBOXES/VIRTUAL/${domain_data}/${local_part_data}


Some hand holding much appreciated .