[exim] recipients_max help

Hello,

I am trying to develop a way to be able to modify max recipients per
email address on our server. So far the recipients_max looks promising.
Would something like this work?

recipients_max = ${if eq {$local_part@$domain}
{lookup{$local_part@$domain}lsearch{/etc/virtual/recipients_max}{$value}} {$value}{150}}*

*where /etc/virtual/recipients_max contains 'email@???: ###'
lines. My goal was anything in the file, if it matches the senders email
address (local emails, sending out, for instance to a mailing list),
uses that value, otherwise the default of 150.

TIA.

Jamey