[exim] dovecot Authentication

Hello. I'm trying to use the dovecot driver in exim but getting a little
stuck.

To be exact, I'm getting an error when trying to authenticate from my IMAP
client (Thunderbird).

The error in the log I get is: "Taint mismatch, string_vformat:
auth_dovecot_server 282".

I think this line in my exim config is the one in question: "server_set_id
= $auth1"

Could you confirm what other tests I could do to ensure the string data for
$auth1 is correct? The error in the log seems like this is an error with
data being passed in? I may be wrong, so any advice is incredibly helpful.

Thank you!