[exim] authentication for system user

hi,
one year ago i prepared a /etc/exim/passwd

user : cryptedpass : ???

and used hash-lookup with crypteq.

but i wanted to change to system-tools, so if a new system user is created
then there should be no need to extend something like password file
anymore.

i tried pam authenticator but i had to open rights to read /etc/shadow for
group
mail (Debian-exim or similiar)

someone told me to use dovecot-sasl-authenticator, so i tried, but i got
following error:

auth_dovecot authenticator failed for klein [172.27.10.97]:50531
I=[172.27.10.97]:25: 435 Unable to authenticate at present: authentication
socket connection error

thanks in advance
andreas