diff --git a/zmldapsync/zmldapsync.pl b/zmldapsync/zmldapsync.pl
index 981f4ec..201cfa7 100755
--- a/zmldapsync/zmldapsync.pl
+++ b/zmldapsync/zmldapsync.pl
@@ -77,7 +77,7 @@ if (not defined $conf->{domains} or ref $conf->{domains} ne 'HASH'){
   exit (0);
 }
 
-DOMAIN: foreach my $domain ( keys $conf->{domains} ) {
+DOMAIN: foreach my $domain ( keys %{$conf->{domains}} ) {
   log_verbose( "Start to process domain $domain" );
 
   # Get default config for this domain and merge it with what we have in the config file
@@ -172,7 +172,7 @@ DOMAIN: foreach my $domain ( keys $conf->{domains} ) {
   # Domain configuration, as defined in the conf
   if (defined $conf->{domains}->{$domain}->{zimbra}->{additional_domain_attrs} ) {
     my $attr_mod = '';
-    foreach my $attr (keys $conf->{domains}->{$domain}->{zimbra}->{additional_domain_attrs} ) {
+    foreach my $attr (keys %{$conf->{domains}->{$domain}->{zimbra}->{additional_domain_attrs}} ) {
       if ( ref $conf->{domains}->{$domain}->{zimbra}->{additional_domain_attrs}->{$attr} eq 'ARRAY' ) {
         my $attr_diff = Array::Diff->diff(
           $domain_entry->{$attr} || [],
@@ -264,15 +264,15 @@ DOMAIN: foreach my $domain ( keys $conf->{domains} ) {
 
   # List of attributes to fetch from LDAP
   # First, we want all the attributes which are mapped to Zimbra fields
-  my $fetch_attrs = [ keys $conf->{domains}->{$domain}->{users}->{attr_map} ];
+  my $fetch_attrs = [ keys %{$conf->{domains}->{$domain}->{users}->{attr_map}} ];
 
   # We also want the object key
-  push $fetch_attrs, $conf->{domains}->{$domain}->{users}->{key};
+  push @{$fetch_attrs}, $conf->{domains}->{$domain}->{users}->{key};
 
   # If defined in the config, we need to get attribute containing email and aliases
   foreach ( qw( alias_attr mail_attr ) ) {
     next if ( not $conf->{domains}->{$domain}->{users}->{$_} );
-    push $fetch_attrs, $conf->{domains}->{$domain}->{users}->{$_};
+    push @{$fetch_attrs}, $conf->{domains}->{$domain}->{users}->{$_};
   }
 
   # Now we can run the lookup
@@ -302,7 +302,7 @@ DOMAIN: foreach my $domain ( keys $conf->{domains} ) {
     filter => '(&(objectClass=zimbraAccount)(!(zimbraIsSystemAccount=TRUE))(!(zimbraIsSystemResource=TRUE)))',
     attrs  => [
       ( map { $conf->{domains}->{$domain}->{users}->{attr_map}->{$_} }
-	       keys $conf->{domains}->{$domain}->{users}->{attr_map} ),
+	       keys %{$conf->{domains}->{$domain}->{users}->{attr_map}} ),
       ( 'uid',
 	'zimbraAccountStatus',
 	'zimbraAuthLdapExternalDn',
@@ -325,7 +325,7 @@ DOMAIN: foreach my $domain ( keys $conf->{domains} ) {
 
   log_verbose( "Comparing the accounts" );
 
-  my @single = keys $conf->{domains}->{$domain}->{users}->{attr_map};
+  my @single = keys %{$conf->{domains}->{$domain}->{users}->{attr_map}};
   push @single, $conf->{domains}->{$domain}->{users}->{mail_attr};
   my $ext_users = ldap2hashref(
     $ext_user_search,
@@ -341,12 +341,12 @@ DOMAIN: foreach my $domain ( keys $conf->{domains} ) {
 
   # First loop : Check users which exist in external LDAP but not in Zimbra
   # or which exist in both but need to be updated
-  foreach my $user ( keys $ext_users ) {
+  foreach my $user ( keys %{$ext_users} ) {
     my $attrs = '';
     if ( defined $zim_users->{$user} ) {
 
       # User exists in Zimbra, lets check its attribute are up to date
-      foreach my $attr ( keys $conf->{domains}->{$domain}->{users}->{attr_map} ) {
+      foreach my $attr ( keys %{$conf->{domains}->{$domain}->{users}->{attr_map}} ) {
 
         if ( not defined $ext_users->{$user}->{$attr} and
              not defined $zim_users->{$user}->{$conf->{domains}->{$domain}->{users}->{attr_map}->{$attr}} ) {
@@ -394,7 +394,7 @@ DOMAIN: foreach my $domain ( keys $conf->{domains} ) {
       # User exists in external LDAP but not in Zimbra. We must create it
       log_verbose( "User $user found in external LDAP but not in Zimbra. Will be created" );
 
-      foreach my $attr ( keys $conf->{domains}->{$domain}->{users}->{attr_map} ) {
+      foreach my $attr ( keys %{$conf->{domains}->{$domain}->{users}->{attr_map}} ) {
         next if (not defined $ext_users->{$user}->{$attr} or $ext_users->{$user}->{$attr} eq '');
         $attrs .= ' ' . $conf->{domains}->{$domain}->{users}->{attr_map}->{$attr} . " " .
                   zim_attr_value( $ext_users->{$user}->{$attr} );
@@ -450,7 +450,7 @@ DOMAIN: foreach my $domain ( keys $conf->{domains} ) {
   }
 
   # Second loop : we loop through the Zimbra users to check if they should be locked (if they don't exist in external LDAP anymore)
-  foreach my $user ( keys $zim_users ) {
+  foreach my $user ( keys %{$zim_users} ) {
     # Make sure we only lock accounts if they don't exist anymore in external LDAP
     # has the zimbraNotes attribute set, with the expected value, and the account is active
     if ( not defined $ext_users->{$user} and
@@ -473,12 +473,12 @@ DOMAIN: foreach my $domain ( keys $conf->{domains} ) {
                $conf->{domains}->{$domain}->{groups}->{filter}
     );
 
-    $fetch_attrs = [ keys $conf->{domains}->{$domain}->{groups}->{attr_map} ];
-    push $fetch_attrs, $conf->{domains}->{$domain}->{groups}->{key};
-    push $fetch_attrs, $conf->{domains}->{$domain}->{groups}->{members_attr};
+    $fetch_attrs = [ keys %{$conf->{domains}->{$domain}->{groups}->{attr_map}} ];
+    push @{$fetch_attrs}, $conf->{domains}->{$domain}->{groups}->{key};
+    push @{$fetch_attrs}, $conf->{domains}->{$domain}->{groups}->{members_attr};
     foreach ( qw( mail_attr alias_attr ) ) {
       next if ( not defined $conf->{domains}->{$domain}->{groups}->{$_} );
-      push $fetch_attrs, $conf->{domains}->{$domain}->{groups}->{$_};
+      push @{$fetch_attrs}, $conf->{domains}->{$domain}->{groups}->{$_};
     }
 
     my $ext_group_search = $ext_ldap->search(
@@ -503,7 +503,7 @@ DOMAIN: foreach my $domain ( keys $conf->{domains} ) {
       filter => "(objectClass=zimbraDistributionList)",
       attrs  => [
         ( map { $conf->{domains}->{$domain}->{groups}->{attr_map}->{$_} }
-            keys $conf->{domains}->{$domain}->{groups}->{attr_map} ),
+            keys %{$conf->{domains}->{$domain}->{groups}->{attr_map}} ),
         (
           'uid',
 	  'zimbraDistributionListSubscriptionPolicy',
@@ -528,7 +528,7 @@ DOMAIN: foreach my $domain ( keys $conf->{domains} ) {
 	         " distribution list(s) in Zimbra" );
     log_verbose( "Comparing groups with distribution lists" );
 
-    my @single = keys $conf->{domains}->{$domain}->{groups}->{attr_map};
+    my @single = keys %{$conf->{domains}->{$domain}->{groups}->{attr_map}};
     push @single, $conf->{domains}->{$domain}->{groups}->{mail_attr};
 
     my $ext_groups = ldap2hashref(
@@ -548,16 +548,16 @@ DOMAIN: foreach my $domain ( keys $conf->{domains} ) {
 
     # Build a dn2id hashref to lookup users or groups by their DN
     my $dn2id = {};
-    $dn2id->{$ext_users->{$_}->{dn}}  = $_ foreach ( keys $ext_users );
-    $dn2id->{$ext_groups->{$_}->{dn}} = $_ foreach ( keys $ext_groups );
+    $dn2id->{$ext_users->{$_}->{dn}}  = $_ foreach ( keys %{$ext_users} );
+    $dn2id->{$ext_groups->{$_}->{dn}} = $_ foreach ( keys %{$ext_groups} );
 
     # First loop, check if every group in LDAP exists as a DL in Zimbra
-    foreach my $group ( keys $ext_groups ) {
+    foreach my $group ( keys %{$ext_groups} ) {
       if ( defined $zim_dl->{$group} ) {
         # A group match an existing DL, we must check its attributes
 
         my $attrs = '';
-        foreach my $attr ( keys $conf->{domains}->{$domain}->{groups}->{attr_map} ) {
+        foreach my $attr ( keys %{$conf->{domains}->{$domain}->{groups}->{attr_map}} ) {
           if ( not defined $ext_groups->{$group}->{$attr} and
                not defined $zim_dl->{$group}->{$conf->{domains}->{$domain}->{groups}->{attr_map}->{$attr}} ) {
             # Attr does not exist in external LDAP and in Zimbra, not need to continue
@@ -603,7 +603,7 @@ DOMAIN: foreach my $domain ( keys $conf->{domains} ) {
         # A new group with no corresponding DL in Zimbra
         log_verbose( "Found a new group : $group. Creating it in Zimbra" );
         my $attrs = '';
-        foreach my $attr ( keys $conf->{domains}->{$domain}->{groups}->{attr_map} ) {
+        foreach my $attr ( keys %{$conf->{domains}->{$domain}->{groups}->{attr_map}} ) {
           next if ( not defined $ext_groups->{$group}->{$attr} or
                     $ext_groups->{$group}->{$attr} eq '');
           $attrs .= ' ' . $conf->{domains}->{$domain}->{groups}->{attr_map}->{$attr} . " " .
@@ -692,7 +692,7 @@ DOMAIN: foreach my $domain ( keys $conf->{domains} ) {
     }
 
     # Now, look at all the distribution list which were created from LDAP but doesn't exist anymore in LDAP
-    foreach my $dl ( keys $zim_dl ) {
+    foreach my $dl ( keys %{$zim_dl} ) {
       next if ( not defined $zim_dl->{$dl}->{zimbraNotes} or
                 $zim_dl->{$dl}->{zimbraNotes} !~ m/^$sync_from_ldap/ );
       next if ( defined $ext_groups->{$dl} );