[Exim] smtp authentication w/ldap - still struggling

i'm still struggling to get smtp authentication working for a virtual
server.. my latest attempt is the following which, in theory, i can't
see why it would fail

the login name is the same as email address, and at times seems to
return correct passwords based on debugging -- but nothing is
authenticating.

fixed_plain:
   driver                 = plaintext
   public_name             = PLAIN
   server_debug_print     = yes
   server_prompts         = :
   server_condition        = ${\
                                   if eq \
                                   {$3}\
                                   {\
                                       ${lookup ldap \
                                               { \
                                                user="cn=Manager,dc=mydomains,dc=com" pass=secret \
                                                   ldap:///\
                                                       ou=Email,o=myserver,dc=mydomains,dc=com\
                                                       ?mobPass\
                                                       ?sub\
                                                       ?(mail=${quote_ldap:$2})\
                                            } \
                                            {$value} \
                                            fail \
                                    } \
                                } \
                                {yes}{no} \
                            }
   server_set_id         = pagan