Starting with Exim 4.94 there’s some breaking changes; the docs say it the best:

Some Transports now refuse to use tainted data in constructing their delivery
location; this WILL BREAK configurations which are not updated accordingly.

So if you are seeing Tainted filename for search or something similar in your logs then that’s the issue.

My Setup

For me personally I was using $domain and $local_part in a router to first find a $domain specific aliases file, then for looking up the destination using $local_part.

My Fix

$domain -> $domain_data

$local_part -> $local_part (this didn’t need changing in my routers data option)

It’s worth looking at the docs to get some ideas about what expansion variables there are.

Hope that helps :)