Complain if the mailbox to be read does not look like a valid mbox-format

mailbox when it is a singular file.

CHANGELOG

@@ -4,6 +4,8 @@ Version 0.4.2   - ???
     with the new option '--date'.
   * Fixed a bug where archivemail would complain about messages older than 
     1970. Yes, someone had a 'Date' header with 1967 :)
+  * Complain if the mailbox to be read does not look like a valid mbox-format
+    mailbox.
 
 Version 0.4.1   - 21 April 2002
   * Don't archive messages that are flagged important unless we are given the

archivemail.py

@@ -924,6 +924,8 @@ def _archive_mbox(mailbox_name, final_archive_name):
     original.procmail_lock()
     original.exclusive_lock()
     msg = original.next()
+    if not msg and (original.starting_size > 0):
+        user_error("'%s' is not a valid mbox-format mailbox" % mailbox_name)
     while (msg):
         stats.another_message()
         vprint("processing message '%s'" % msg.get('Message-ID'))