Index: app/models/mailer.rb
===================================================================
--- app/models/mailer.rb	(リビジョン 17872)
+++ app/models/mailer.rb	(作業コピー)
@@ -721,7 +721,7 @@
     hash = [
       "redmine",
       "#{object.class.name.demodulize.underscore}-#{object.id}",
-      timestamp.strftime("%Y%m%d%H%M%S")
+      timestamp.utc.strftime("%Y%m%d%H%M%S")
     ]
     if rand
       hash << Redmine::Utils.random_hex(8)
Index: test/unit/mailer_test.rb
===================================================================
--- test/unit/mailer_test.rb	(リビジョン 17872)
+++ test/unit/mailer_test.rb	(作業コピー)
@@ -340,6 +340,15 @@
     end
   end
 
+  def test_timestamp_in_message_id_should_be_utc
+    current_zone = Time.zone
+    %w(UTC Paris Tokyo).each do |zone|
+      Time.zone = zone
+      assert_match /redmine.issue-3.20060719190727.[0-9a-f]+@example.net/, Mailer.token_for(Issue.find(3))
+    end
+    Time.zone = current_zone
+  end
+
   test "#issue_add should notify project members" do
     issue = Issue.find(1)
     assert Mailer.deliver_issue_add(issue)