diff --git a/lib/MT/ConfigMgr.pm b/lib/MT/ConfigMgr.pm
index 5c9efdbf77..efd11b6c06 100644
--- a/lib/MT/ConfigMgr.pm
+++ b/lib/MT/ConfigMgr.pm
@@ -24,6 +24,7 @@ sub new {
         __paths             => [],
         __dirty             => 0,
         __overwritable_keys => {},
+        __env               => {},
         },
         $_[0];
     $mgr->init;
@@ -31,6 +32,14 @@ sub new {
 }
 
 sub init {
+    my $mgr = shift;
+    for my $key (grep /^MT_CONFIG_/i, keys %ENV) {
+        (my $name = $key) =~ s/^MT_CONFIG_//i;
+        $name =~ s/_//g;
+        my $value = $ENV{$key};
+        $value = '' if $value eq q{''};
+        $mgr->{__env}{lc $name} = $value;
+    }
 }
 
 sub define {
@@ -95,6 +104,8 @@ sub get_internal {
         return $mgr->get($alias);
     }
 
+    return $mgr->{__env}{$var} if exists $mgr->{__env}{$var};
+
     $val = $mgr->{__dbvar}{$var} if $mgr->is_overwritable($var);
     $val = $mgr->{__var}{$var} unless defined($val);
     $val = { %{ $mgr->{__dbvar}{$var} }, %$val } if ($mgr->type($var) eq 'HASH' && $val && $mgr->{__dbvar}{$var});
@@ -110,6 +121,7 @@ sub get_internal {
 sub get {
     my $mgr = shift;
     my $var = lc shift;
+    return $mgr->{__env}{$var} if exists $mgr->{__env}{$var};
     if ( my $h = $mgr->{__settings}{$var}{handler} ) {
         $h = MT->handler_to_coderef($h) unless ref $h;
         return $h->($mgr);
@@ -151,6 +163,7 @@ sub set_internal {
     my $mgr = shift;
     my ( $var, $val, $db_flag ) = @_;
     $var = lc $var;
+    return $mgr->{__env}{$var} if exists $mgr->{__env}{$var};
     $mgr->set_dirty() if defined($db_flag) && $db_flag;
     my $set = $db_flag ? '__dbvar' : '__var';
     if ( defined( my $alias = $mgr->{__settings}{$var}{alias} ) ) {
@@ -194,6 +207,7 @@ sub set {
     my $mgr = shift;
     my ( $var, $val, $db_flag ) = @_;
     $var = lc $var;
+    return $mgr->{__env}{$var} if exists $mgr->{__env}{$var};
     $mgr->set_dirty($var);
     if ( my $h = $mgr->{__settings}{$var}{handler} ) {
         $h = MT->handler_to_coderef($h) unless ref $h;
diff --git a/php/mt.php b/php/mt.php
index d5f1587dae..e1693f50ae 100644
--- a/php/mt.php
+++ b/php/mt.php
@@ -49,6 +49,7 @@ class MT {
     protected $blog_id;
     protected $db;
     protected $config;
+    protected $config_env;
     protected $debugging = false;
     protected $caching = false;
     protected $conditional = false;
@@ -127,6 +128,7 @@ function init($blog_id = null, $cfg_file = null) {
         }
 
         $this->configure($cfg_file);
+        $this->configure_from_env();
         $this->init_addons();
         $this->configure_from_db();
 
@@ -286,6 +288,9 @@ public function clear_cache_driver() {
 
     public function config($id, $value = null) {
         $id = strtolower($id);
+        if (isset($this->config_env[$id])) {
+            return $this->config_env[$id];
+        }
         if (isset($value))
             $this->config[$id] = $value;
         return isset($this->config[$id]) ? $this->config[$id] : null;
@@ -389,6 +394,22 @@ function configure($file = null) {
         }
     }
 
+    function configure_from_env() {
+        $cfg =& $this->config_env;
+        foreach(array_keys($_ENV) as $i => $name) {
+            $lc_name = strtolower($name);
+            if (strpos($lc_name, 'mt_config_') === 0) {
+                $lc_name = preg_replace('/^mt_config_/', '', $lc_name);
+                $lc_name = preg_replace('/_/', '', $lc_name);
+                $value = $_ENV[$name];
+                if (isset($value) && $value === "''") {
+                    $value = '';
+                }
+                $cfg[$lc_name] = $value;
+            }
+        }
+    }
+
     function configure_from_db() {
         $cfg =& $this->config;
         $mtdb =& $this->db();
diff --git a/t/tag/config_env.t b/t/tag/config_env.t
new file mode 100644
index 0000000000..c16aee8e7a
--- /dev/null
+++ b/t/tag/config_env.t
@@ -0,0 +1,65 @@
+use strict;
+use warnings;
+use FindBin;
+use lib "$FindBin::Bin/../lib";    # t/lib
+use Test::More;
+use MT::Test::Env;
+our $test_env;
+
+BEGIN {
+    $test_env = MT::Test::Env->new;
+    $ENV{MT_CONFIG} = $test_env->config_file;
+
+    # config directive set by MT::Test::Env
+    $ENV{MT_CONFIG_EMAIL_ADDRESS_MAIN} = 'mt_test@localhost.localdomain';
+
+    # config directive that has a default value
+    $ENV{MT_CONFIG_CMSSEARCHLIMIT} = 1000;
+
+    # config_directive that has no default value
+    $ENV{MT_CONFIG_RsyncOptions} = '-v';
+}
+
+use MT::Test::PHP;
+use MT::Test::Tag;
+
+$test_env->prepare_fixture('db');
+
+my $cnf = MT->config;
+is $cnf->EmailAddressMain => $ENV{MT_CONFIG_EMAIL_ADDRESS_MAIN}, "EmailAddressMain is overriden by the env";
+is $cnf->CMSSearchLimit   => $ENV{MT_CONFIG_CMSSEARCHLIMIT},     "CMSSearchLimit is overriden by the env";
+is $cnf->RsyncOptions     => $ENV{MT_CONFIG_RsyncOptions},       "RsyncOptions is overriden by the env";
+
+$cnf->EmailAddressMain('something different', 1);
+$cnf->CMSSearchLimit('something different', 1);
+$cnf->RsyncOptions('something different', 1);
+$cnf->save_config;
+
+is $cnf->EmailAddressMain => $ENV{MT_CONFIG_EMAIL_ADDRESS_MAIN}, "EmailAddressMain is still overriden by the env";
+is $cnf->CMSSearchLimit   => $ENV{MT_CONFIG_CMSSEARCHLIMIT},     "CMSSearchLimit is still overriden by the env";
+is $cnf->RsyncOptions     => $ENV{MT_CONFIG_RsyncOptions},       "RsyncOptions is still overriden by the env";
+
+MT::Test::Tag->run_perl_tests(1);
+MT::Test::Tag->run_php_tests(1);
+
+done_testing;
+
+__DATA__
+
+=== env with underscores
+--- template
+<mt:var name="config.EmailAddressMain">
+--- expected eval
+$ENV{MT_CONFIG_EMAIL_ADDRESS_MAIN}
+
+=== env without underscores
+--- template
+<mt:var name="config.CMSSearchLimit">
+--- expected eval
+$ENV{MT_CONFIG_CMSSEARCHLIMIT}
+
+=== env with mixed cases
+--- template
+<mt:var name="config.RsyncOptions">
+--- expected eval
+$ENV{MT_CONFIG_RsyncOptions}