[exim] Optional from exim 3?

Hej everyone

I need a hint.

In my old exim 3 config i use the keyword optional when trying to open
files. By having optinal exim defers instead of causing a fail

But in exim4 im missing the optional, my config looks like this:

virtual_domain_aliases:
driver = redirect
qualify_preserve_domain
allow_fail
allow_defer
domains = lsearch;/etc/exim/domains/virtual
data = ${lookup{$local_part}lsearch{/etc/exim/aliases/${domain_data}}}


The problem occurs when trying to lsearch af file which doesn't exists.
What can be added to allow "file access failure" eg. could also be a
database down og something like that

--
Med venlig hilsen/Best regards
Lasse Birnbaum Jensen