[Exim] The same password for POP3 & SMTP? (Exim 3.35)

Hello

I allow users to change their "pop3 passwords" by setting their shell
to /bin/passwd and letting them connect with ssh.
However, due to:

login:
driver = plaintext
public_name = LOGIN
server_prompts = "Username:: : Password::"
server_condition = "${if crypteq{$2}{${extract{1}{:}{${lookup{$1}lsearch{/etc/exim/passwd}{$value}{*:*}}}}}{1}{0}}"
server_set_id = $1

in my exim.conf file, the "smtp password" I set up with htpasswd
remains unchanged.
What is the easiest way to assure that both the passwords are the same
and letting users to change them? (No login shells given...!)

thanks
mike