Index: app/models/mailer.rb
===================================================================
--- app/models/mailer.rb	(revision 2761)
+++ app/models/mailer.rb	(working copy)
@@ -245,6 +245,7 @@
   # for the case of plain text only
   def body(*params)
     value = super(*params)
+    subject "=?#{charset}?B?#{Base64.encode64(subject)}?="
     if Setting.plain_text_mail?
       templates = Dir.glob("#{template_path}/#{@template}.text.plain.{rhtml,erb}")
       unless String === @body or templates.empty?