[exim] Deprecated pam_stack module called from service "exim…

I'm using the following authenticator with Exim 4.62 on FC5 (kernel 2.6.16):

auth_login:
driver = plaintext
public_name = LOGIN
server_prompts = Username:: : Password::
server_condition = ${if saslauthd{{$1}{$2}{exim}}{1}{0}}
server_set_id = $1

I keep getting the following warnings into the system log:
Deprecated pam_stack module called from service "exim"

This warning looks to me, that Exim is now using some to-be-obsoleted
method to authenticate the user in question. Is there some other
preferred way to verify the usernames and passwords?


Regards,
Timo