[exim] Using in different auth sources in parallel

Hi,

I currently offer standard LOGIN authentication to my SMTP server using
a few standard passwords from /etc/exim/passwd

I use the default code from Debian exim4 config for this:

login_server:
driver = plaintext
public_name = LOGIN
server_prompts = "Username:: : Password::"
server_condition = "${if
crypteq{$auth2}{${extract{1}{:}{${lookup{$auth1}lsearch{CONFDIR/passwd}{$value}{*:*}}}}}{1}{0}}"
server_set_id = $auth1
.ifndef AUTH_SERVER_ALLOW_NOTLS_PASSWORDS
server_advertise_condition = ${if eq{$tls_cipher}{}{}{*}}
.endif

Now I want to add support for logging in with the credentials from dovecot:

login_dovecot_authdaemon:
driver = dovecot
public_name = PLAIN
server_socket = /var/run/dovecot/auth-client
server_set_id = $auth1
.ifndef AUTH_SERVER_ALLOW_NOTLS_PASSWORDS
server_advertise_condition = ${if eq{$tls_cipher}{}{}{*}}
.endif

When I enable both of them I unfortunately get:

2011-02-23 16:52:09 Exim configuration error:
two server authenticators (login_server and login_dovecot_authdaemon)
have the same public name (LOGIN)

However, for the first time I want to enable *both* sources. The first
one for people who have already configured their client using the
current passwords.

And the second (dovecot) one for when setting up new users.

Is this somehow possible? Either try login_dovecot_authdaemon when
login_server fails or the other way round?

Regards,
Luke