[exim] Ldap_default_servers setting

I am trying to set the ldap_default_servers value to

${extract{4}{ }{${extract{1}{:}{${lookup dnsdb{>:
srv=_gc._tcp.nhm.ac.uk}{$value}fail}}}}}:${extract{3}{
}{${extract{1}{:}{${lookup d
nsdb{>: srv=_gc._tcp.nhm.ac.uk}{$value}fail}}}}}

and have in my configuration file

ldap_default_servers = ${extract{4}{ }{${extract{1}{:}{${lookup dnsdb{>:
srv=_gc._tcp.nhm.ac.uk}{$value}fail}}}}}:${extract{3}{
}{${extract{1}{:}{${lookup d
nsdb{>: srv=_gc._tcp.nhm.ac.uk}{$value}fail}}}}}

However testing this file yeilds:

17:46:10  8865 perform_ldap_search: ldap URL =
"ldap:///DC=nhm,DC=ac,DC=uk?sAMAccountName?sub?(&(proxyAddresses=SMTP:r.
bannocks%40nhm.ac.uk)(&(objectclass=person)(msExchUserAccountControl=0))
)" server={${extract{4}{ }{${extract{1}{ port=0 sizelimit=0 timelimit=0
tcplimit=0
17:46:10  8865 after ldap_url_parse: host={${extract{4}{ }{${extract{1}{
port=0
17:46:10  8865 initialized for LDAP (v3) server {${extract{4}{
}{${extract{1}{:389
17:46:10  8865 binding with user=LDAPACCT password=LDAPPASS
17:46:10  8865 failed to bind the LDAP connection to server
{${extract{4}{ }{${extract{1}{:389 - ldap_bind() returned -1
17:46:10  8865 perform_ldap_search: ldap URL =
"ldap:///DC=nhm,DC=ac,DC=uk?sAMAccountName?sub?(&(proxyAddresses=SMTP:r.
bannocks%40nhm.ac.uk)(&(objectclass=person)(msExchUserAccountControl=0))
)" server=}{${lookup dnsdb{> port=0 sizelimit=0 timelimit=0 tcplimit=0
17:46:10  8865 after ldap_url_parse: host=}{${lookup dnsdb{> port=0
17:46:10  8865 initialized for LDAP (v3) server }{${lookup dnsdb{>:389
17:46:10  8865 binding with user=LDAPACCT password=LDAPPASS
17:46:10  8865 failed to bind the LDAP connection to server }{${lookup
dnsdb{>:389 - ldap_bind() returned -1
17:46:10  8865 perform_ldap_search: ldap URL =
"ldap:///DC=nhm,DC=ac,DC=uk?sAMAccountName?sub?(&(proxyAddresses=SMTP:r.
bannocks%40nhm.ac.uk)(&(objectclass=person)(msExchUserAccountControl=0))
)" server=srv=_gc._tcp.nhm.ac.uk}{$value}fail}}}}} port=0 sizelimit=0
timelimit=0 tcplimit=0
17:46:10  8865 after ldap_url_parse:
host=srv=_gc._tcp.nhm.ac.uk}{$value}fail}}}}} port=0
17:46:10  8865 initialized for LDAP (v3) server
srv=_gc._tcp.nhm.ac.uk}{$value}fail}}}}}:389
17:46:10  8865 binding with user=LDAPACCT password=LDAPPASS
17:46:10  8865 failed to bind the LDAP connection to server
srv=_gc._tcp.nhm.ac.uk}{$value}fail}}}}}:389 - ldap_bind() returned -1
17:46:10  8865 perform_ldap_search: ldap URL =
"ldap:///DC=nhm,DC=ac,DC=uk?sAMAccountName?sub?(&(proxyAddresses=SMTP:r.
bannocks%40nhm.ac.uk)(&(objectclass=person)(msExchUserAccountControl=0))
)" server=${extract{3}{ }{${extract{1}{ port=0 sizelimit=0 timelimit=0
tcplimit=0
17:46:10  8865 after ldap_url_parse: host=${extract{3}{ }{${extract{1}{
port=0
17:46:10  8865 initialized for LDAP (v3) server ${extract{3}{
}{${extract{1}{:389
17:46:10  8865 binding with user=LDAPACCT password=LDAPPASS
17:46:10  8865 failed to bind the LDAP connection to server
${extract{3}{ }{${extract{1}{:389 - ldap_bind() returned -1
17:46:10  8865 perform_ldap_search: ldap URL =
"ldap:///DC=nhm,DC=ac,DC=uk?sAMAccountName?sub?(&(proxyAddresses=SMTP:r.
bannocks%40nhm.ac.uk)(&(objectclass=person)(msExchUserAccountControl=0))
)" server=}{${lookup dnsdb{> port=0 sizelimit=0 timelimit=0 tcplimit=0
17:46:10  8865 after ldap_url_parse: host=}{${lookup dnsdb{> port=0
17:46:10  8865 re-using cached connection to LDAP server }{${lookup
dnsdb{>:389
17:46:10  8865 binding with user=LDAPACCT password=LDAPPASS
17:46:10  8865 failed to bind the LDAP connection to server }{${lookup
dnsdb{>:389 - ldap_bind() returned -1
17:46:10  8865 perform_ldap_search: ldap URL =
"ldap:///DC=nhm,DC=ac,DC=uk?sAMAccountName?sub?(&(proxyAddresses=SMTP:r.
bannocks%40nhm.ac.uk)(&(objectclass=person)(msExchUserAccountControl=0))
)" server=srv=_gc._tcp.nhm.ac.uk}{$value}fail}}}}}} port=0 sizelimit=0
timelimit=0 tcplimit=0
17:46:10  8865 after ldap_url_parse:
host=srv=_gc._tcp.nhm.ac.uk}{$value}fail}}}}}} port=0
17:46:10  8865 initialized for LDAP (v3) server
srv=_gc._tcp.nhm.ac.uk}{$value}fail}}}}}}:389
17:46:10  8865 binding with user=LDAPACCT password=LDAPPASS
17:46:10  8865 failed to bind the LDAP connection to server
srv=_gc._tcp.nhm.ac.uk}{$value}fail}}}}}}:389 - ldap_bind() returned -1
17:46:10  8865 lookup deferred: failed to bind the LDAP connection to
server srv=_gc._tcp.nhm.ac.uk}{$value}fail}}}}}}:389 - ldap_bind()
returned -1
17:46:10  8865 failed to expand: ${lookup ldap { user=LDAPACCT
pass=LDAPPASS
ldap:///DC=nhm,DC=ac,DC=uk?sAMAccountName?sub?(&(proxyAddresses=SMTP:${q
uote_ldap:$local_part@???})(&(objectclass=person)(msExchUserAccoun
tControl=0)))}}
17:46:10  8865    error message: lookup of "user=LDAPACCT pass=LDAPPASS
ldap:///DC=nhm,DC=ac,DC=uk?sAMAccountName?sub?(&(proxyAddresses=SMTP:r.b
annocks%40nhm.ac.uk)(&(objectclass=person)(msExchUserAccountControl=0)))
" gave DEFER: failed to bind the LDAP connection to server
srv=_gc._tcp.nhm.ac.uk}{$value}fail}}}}}}:389 - ldap_bind() returned -1
17:46:10  8865 condition check lookup defer
r.bannocks@??? cannot be resolved at this time:
  condition check lookup defer
17:46:10  8865 search_tidyup called
17:46:10  8865 unbind LDAP connection to
srv=_gc._tcp.nhm.ac.uk}{$value}fail}}}}}}:389
17:46:10  8865 unbind LDAP connection to ${extract{3}{
}{${extract{1}{:389
17:46:10  8865 unbind LDAP connection to
srv=_gc._tcp.nhm.ac.uk}{$value}fail}}}}}:389
17:46:10  8865 unbind LDAP connection to }{${lookup dnsdb{>:389
17:46:10  8865 unbind LDAP connection to {${extract{4}{
}{${extract{1}{:389
17:46:10  8865 >>>>>>>>>>>>>>>> Exim pid=8865 terminating with rc=1

>>>>>>>>>>>>>>>>


So it looks as though the string is being interpreted literally for some
reason. Have I got the syntax right?

Any assistance appreciated.

RB