diff --git a/lib/sup/maildir.rb b/lib/sup/maildir.rb
index 28b433ed..1883844a 100644
--- a/lib/sup/maildir.rb
+++ b/lib/sup/maildir.rb
@@ -114,6 +114,10 @@ def raw_message id
     with_file_for(id) { |f| f.read }
   end
 
+  def fallback_date_for_message id
+    File.mtime File.join(@dir, id)
+  end
+
   ## XXX use less memory
   def poll
     added = []
diff --git a/lib/sup/mbox.rb b/lib/sup/mbox.rb
index 61a220ec..ec931e34 100644
--- a/lib/sup/mbox.rb
+++ b/lib/sup/mbox.rb
@@ -1,5 +1,6 @@
 require 'uri'
 require 'set'
+require 'time'
 
 module Redwood
 
@@ -137,6 +138,26 @@ def each_raw_message_line offset
     end
   end
 
+  def fallback_date_for_message offset
+    ## This is a bit awkward... We treat the From line as a delimiter,
+    ## not part of the message. So the offset is pointing *after* the
+    ## From line for the desired message. With a bit of effort we can
+    ## scan backwards to find its From line and extract a date from it.
+    buf = @mutex.synchronize do
+      ensure_open
+      start = offset
+      loop do
+        start = (start - 200).clamp 0, 2**64
+        @f.seek start
+        buf = @f.read (offset - start)
+        break buf if buf.include? ?\n or start == 0
+      end
+    end
+    BREAK_RE.match buf.lines.last do |m|
+      Time.strptime m[1], "%a %b %d %H:%M:%S %Y"
+    end
+  end
+
   def default_labels
     [:inbox, :unread]
   end
diff --git a/lib/sup/message.rb b/lib/sup/message.rb
index 6ee18537..0a0bcc6e 100644
--- a/lib/sup/message.rb
+++ b/lib/sup/message.rb
@@ -103,16 +103,10 @@ def parse_header encoded_header
     when Time
       date
     when String
-      begin
-        Time.parse date
-      rescue ArgumentError
-        #debug "faking mangled date header for #{@id} (orig #{header['date'].inspect} gave error: #{e.message})"
-        Time.now
-      end
-    else
-      #debug "faking non-existent date header for #{@id}"
-      Time.now
+      Time.parse date rescue nil
     end
+    @date = location.fallback_date if @date.nil?
+    @date = Time.utc 1970, 1, 1 if @date.nil?
 
     subj = header["subject"]
     subj = subj ? subj.fix_encoding! : nil
@@ -808,6 +802,10 @@ def parsed_message
     source.load_message info
   end
 
+  def fallback_date
+    source.fallback_date_for_message info
+  end
+
   def valid?
     source.valid? info
   end
diff --git a/test/dummy_source.rb b/test/dummy_source.rb
index ac907a23..d8515313 100644
--- a/test/dummy_source.rb
+++ b/test/dummy_source.rb
@@ -59,6 +59,10 @@ def each_raw_message_line id
       end
     end
   end
+
+  def fallback_date_for_message id
+    Time.utc 2001, 2, 3, 4, 56, 57
+  end
 end
 
 end
diff --git a/test/integration/test_maildir.rb b/test/integration/test_maildir.rb
index 2211b440..9249227a 100644
--- a/test/integration/test_maildir.rb
+++ b/test/integration/test_maildir.rb
@@ -34,7 +34,9 @@ def create_a_maildir(extra='')
   end
 
   def create_a_maildir_email(folder, content)
-    File.write(File.join(folder, "#{Time.now.to_f}.hostname:2,S"), content)
+    filename = File.join folder, "#{Time.now.to_f}.hostname:2,S"
+    File.write filename, content
+    filename
   end
 
   def start_sup_and_add_source(source)
@@ -74,5 +76,17 @@ def test_can_index_a_maildir_directory_with_special_characters
 
   end
 
+  def test_missing_date_header
+    ## The message is missing a Date header so we should use its modtime
+    ## as a fallback.
+    fallback_date = Time.new 2004, 4, 19, 11, 12, 13
+    maildir = create_a_maildir
+    filename = create_a_maildir_email(File.join(maildir, 'cur'), @test_message_1)
+    File.utime fallback_date, fallback_date, filename
+    start_sup_and_add_source Maildir.new "maildir:#{maildir}"
+
+    messages_in_index = Index.instance.enum_for(:each_message).to_a
+    assert_equal fallback_date, messages_in_index.first.date
+  end
 end
 
diff --git a/test/integration/test_mbox.rb b/test/integration/test_mbox.rb
index 421b86a7..ebd6076d 100644
--- a/test/integration/test_mbox.rb
+++ b/test/integration/test_mbox.rb
@@ -69,4 +69,14 @@ def test_can_index_a_mbox_directory_with_special_characters
 
   end
 
+  def test_missing_date_header
+    ## The message is missing a Date header so we should use envelope date
+    ## stored in the From line as a fallback.
+    fallback_date = Time.new 2009, 4, 27, 12, 56, 18
+    mbox = create_a_mbox
+    start_sup_and_add_source MBox.new "mbox:#{mbox}"
+
+    messages_in_index = Index.instance.enum_for(:each_message).to_a
+    assert_equal fallback_date, messages_in_index.first.date
+  end
 end