Index: lib/sup/maildir.rb
===================================================================
--- lib/sup/maildir.rb	(revision 503)
+++ lib/sup/maildir.rb	(working copy)
@@ -31,7 +31,7 @@
 
   def check
     scan_mailbox
-    start = @ids.index(cur_offset || start_offset) or raise OutOfSyncSourceError, "Unknown message id #{cur_offset || start_offset}." # couldn't find the most recent email
+    start = @ids.index(cur_offset || start_offset) or raise OutOfSyncSourceError, "Unknown message id #{cur_offset || start_offset}." unless @ids.empty? # couldn't find the most recent email
   end
 
   def load_header id
@@ -87,9 +87,7 @@
   end
 
   def each
-    scan_mailbox
-    start = @ids.index(cur_offset || start_offset) or raise OutOfSyncSourceError, "Unknown message id #{cur_offset || start_offset}." # couldn't find the most recent email
-
+    check
     start.upto(@ids.length - 1) do |i|         
       id = @ids[i]
       self.cur_offset = id
@@ -99,12 +97,12 @@
 
   def start_offset
     scan_mailbox
-    @ids.first
+    @ids.first || 0
   end
 
   def end_offset
     scan_mailbox
-    @ids.last
+    @ids.last || 0
   end
 
   def pct_done; 100.0 * (@ids.index(cur_offset) || 0).to_f / (@ids.length - 1).to_f; end