diff --git a/actionmailer/CHANGELOG b/actionmailer/CHANGELOG
index 7254016a612..45283d11a98 100644
--- a/actionmailer/CHANGELOG
+++ b/actionmailer/CHANGELOG
@@ -1,3 +1,8 @@
+*SVN*
+
+* Stricter matching for implicitly multipart filenames excludes files ending in unsupported extensions (such as foo.rhtml.bak) and without a two-part content type (such as foo.text.rhtml or foo.text.really.plain.rhtml).  #2398 [Dave Burt <dave@burt.id.au>, Jeremy Kemper]
+
+
 *1.1.3* (November 7th, 2005)
 
 * Allow Mailers to have custom initialize methods that set default instance variables for all mail actions #2563 [mrj@bigpond.net.au]
diff --git a/actionmailer/lib/action_mailer/base.rb b/actionmailer/lib/action_mailer/base.rb
index cc996790c8a..8659489808b 100644
--- a/actionmailer/lib/action_mailer/base.rb
+++ b/actionmailer/lib/action_mailer/base.rb
@@ -278,11 +278,13 @@ module ActionMailer
         if @parts.empty?
           templates = Dir.glob("#{template_path}/#{@template}.*")
           templates.each do |path|
-            type = (File.basename(path).split(".")[1..-2] || []).join("/")
-            next if type.empty?
-            @parts << Part.new(:content_type => type,
+            # TODO: don't hardcode rhtml|rxml
+            next unless md = /^([^\.]+)\.([^\.]+\.[^\+]+)\.(rhtml|rxml)$/.match(File.basename(path))
+            template_name = "#{md.captures[0]}.#{md.captures[1]}"
+            content_type = md.captures[1].gsub('.', '/')
+            @parts << Part.new(:content_type => content_type,
               :disposition => "inline", :charset => charset,
-              :body => render_message(File.basename(path).split(".")[0..-2].join('.'), @body))
+              :body => render_message(template_name, @body))
           end
           unless @parts.empty?
             @content_type = "multipart/alternative"
diff --git a/actionmailer/test/fixtures/test_mailer/implicitly_multipart_example.ignored.rhtml b/actionmailer/test/fixtures/test_mailer/implicitly_multipart_example.ignored.rhtml
new file mode 100644
index 00000000000..6940419d47a
--- /dev/null
+++ b/actionmailer/test/fixtures/test_mailer/implicitly_multipart_example.ignored.rhtml
@@ -0,0 +1 @@
+Ignored when searching for implicitly multipart parts.
diff --git a/actionmailer/test/fixtures/test_mailer/implicitly_multipart_example.rhtml.bak b/actionmailer/test/fixtures/test_mailer/implicitly_multipart_example.rhtml.bak
new file mode 100644
index 00000000000..6940419d47a
--- /dev/null
+++ b/actionmailer/test/fixtures/test_mailer/implicitly_multipart_example.rhtml.bak
@@ -0,0 +1 @@
+Ignored when searching for implicitly multipart parts.